Wood movement is the natural expansion and contraction of wood because of changes in moisture and humidity. Professional woodworkers who understand how wood behaves rarely run into problems, even after working with it for decades.
Today, Flowyline explains:
- How wood expands and contracts
- How to calculate the amount of movement using a wood movement calculator
- How to design furniture and projects that account for this movement
As you're new to woodworking, this whole concept can feel intimidating. So let's break it down!
What is Wood Movement?
Wood movement is when wood expands and contracts based on the moisture in the air around it. Wood is hygroscopic, which means it constantly absorbs and releases moisture from the air. This is different from materials like metal or plastic, which don't do this.
How Does Wood Movement Work: At a Microscopic Level
When you first cut down a tree, it's loaded with water. We call this "green" wood that contains moisture in two forms:
- Free water: The liquid sitting in the cell cavities and pores
- Bound water: Moisture chemically held within the cell walls themselves
The total moisture content varies widely by species and can range from around 35% to over 200%.
As the wood dries, the free water leaves first. During this phase, nothing really happens. The wood stays the same size.
But once the wood reaches what's called the fiber saturation point (around 26 — 30% moisture content), all the free water is gone. Below this threshold, bound water starts leaving the cell walls. At the same time, the wood begins to shrink and expand.
It's pretty similar to a kitchen sponge. A dry sponge is small and hard. Add water, and it swells up. Wood does the same thing. The fibers swell when they absorb moisture and shrink when they release it.
And, this process never stops. Even after you kiln-dry lumber down to 6 — 8% moisture (or air-dry it to 9 — 12%), the wood keeps exchanging moisture with whatever room it's sitting in. Forever.
This is why your grandmother's dresser drawers stick like crazy in August but glide perfectly in January. Humidity goes up, wood swells. Humidity drops, wood shrinks.
Once you understand this wood movement, you can actually plan for it. And that's what the rest of this guide is about.
Understanding Equilibrium Moisture Content (EMC)
So, there's this thing called Equilibrium Moisture Content, or EMC. It's when wood stops absorbing or releasing moisture because it's matched up with the air around it. Balanced out.
However, EMC isn't static. It changes with the seasons.
The relationship between relative humidity and wood moisture content follows predictable patterns, but it's not perfectly linear. Here's what you need to know:
Most North American homes fluctuate between 25% and 65% relative humidity throughout the year. This seasonal swing causes wood moisture content to change by about 6%.
To understand how this affects your projects: A 4% change in moisture content will cause wood to shrink or expand about 1% across the grain. That means a 12-inch-wide tabletop could change by about 1/8 to 1/4 inch depending on the wood species.
If you're in most parts of North America, here's what happens throughout the year:
- Summer (high humidity) = Higher EMC = Wood expanding
- Winter (low humidity) = Lower EMC = Wood contracting
This seasonal back and forth is what causes all that movement in furniture, cabinets, and flooring. Still, it's completely predictable. Thus, we can plan for it.
Flat-Sawn vs Quarter-Sawn: Why Grain Orientation Matters
Not all boards move the same amount, even if they're the same species and width. How the board was cut from the log makes a huge difference in wood movement.
- Flat-sawn boards move more across their width.
- Quarter-sawn boards move more through their thickness.
Flat-sawn vs quarter-sawn: It matters to wood movement
Photo: RHMB
We'll break down exactly why that happens in this section.
1. Flat-Sawn (Plain-Sawn) Lumber
Look at the end grain of a flat-sawn board, and you'll see growth rings running horizontally across the width. They look like arches or U-shapes.
- These boards move tangentially, which means they have the most dramatic movement of any cut.
- It’s about 40 — 50% more movement compared to quarter-sawn lumber. Some species move nearly twice as much, but it varies.
- As the wood dries, it tends to cup in the opposite direction of the growth rings.
- Besides, flat-sawn is more common and usually more budget-friendly, which is why you see it everywhere.
Flat sawn is an inexpensive option compared to quarter sawn because it’s easier to obtain
Photo: RHMB
2. Quarter-Sawn (Rift-Sawn) Lumber
Quarter-sawn boards have growth rings running vertically, perpendicular to the face of the board.
- These move radially, which makes them way more stable.
- You get 40 — 50% less width movement compared to flat-sawn lumber.
- They stay flat and resist cupping, which is why furniture makers love them.
- The larger tangential movement gets redirected to the board's thickness, where the actual change is much smaller. (since thickness is only 1" vs 12" width).
- The only downside is that they're more expensive and sometimes harder to track down. But, if you're building fine furniture, quarter-sawn is what you want.
Quartersawn lumber comes at a premium due to the labor it takes to mill each plank
Photo: RHMB
3. The Numbers in a Wood Expansion Chart
When you look at a wood movement chart, you'll see two numbers listed for each species.
- Tangential Coefficient (CT) for flat-sawn lumber
- Radial Coefficient (CR) for quarter-sawn lumber.
We take walnut, for example:
- The tangential coefficient is 0.00274
- The radial is 0.00190
That means flat-sawn walnut moves about 1.4 times as much as quarter-sawn walnut. On a 40-inch tabletop with an 8% seasonal moisture change.
- Flat-sawn walnut: 40 × 0.00274 × 8 = 0.876 inches (~7/8")
- Quarter-sawn walnut: 40 × 0.00190 × 8 = 0.608 inches (~5/8")
You see, that quarter-inch difference is huge when you're working with fine tolerances.
Pro tips: If you're building something where stability really matters (fine furniture, cabinet doors, drawer fronts), it's recommended to go with quarter-sawn lumber whenever you can afford it.
Which Direction Does Wood Move?
Wood moves in 3 directions, but the amount of movement varies wildly depending on which direction we're talking about.
1. Tangential (Along the Growth Rings): The Greatest Wood Movement
This is the big wood movement one, which is up to 8% shrinkage when wood goes from green to fully dried.
Tangential movement follows the curve of the annual growth rings. If you look at the end of a board, you'll see those curved lines. The movement happens along those curves.
Flat-sawn lumber (sometimes called plain-sawn) moves mostly in this tangential direction. Why? Because the growth rings run more or less horizontally across the width of the board.
Remember flat-sawn lumber from earlier? Those boards with horizontal growth rings move primarily in this tangential direction. That's why flat-sawn boards move so much across their width.
2. Radial (Across the Growth Rings): Half Movement of Tangential
Secondly, radial movement goes perpendicular to the growth rings. We can think of it like the radius of a circle, extending outward from the center of the tree.
This type of wood movement is usually around 4% shrinkage, which is about half of what you get with tangential movement.
Quarter-sawn lumber moves mostly in this radial direction because the growth rings run vertically through the board. Since radial movement is smaller, quarter-sawn boards are more stable across their width.
3. Longitudinal (Along the Length): Very Little Movement
Thirdly, wood barely moves along its length at all. That's only 0.01% shrinkage, which is basically nothing.
An 8-foot board will only shift about 3/32 inch along its entire length. That's why most woodworkers don't even bother accounting for longitudinal wood movement when they're planning a project. It's just not worth worrying about.
So, when you're planning wood movement furniture or any woodworking project, you only need to worry about movement going across the width. Length? Forget about it. It's negligible.
3 Factors that Affect Wood Movement
Understanding wood movement isn't just about knowing that wood expands and contracts. You need to understand why it happens and how much movement to expect. Three key factors determine how your wood will behave:
1. Humidity: The Primary Driver of Woods Air Movement
In fact, humidity is the #1 cause of wood movement. But here's where people get confused. There are actually 2 different ways to measure humidity, and you need to understand both.
- Relative humidity (RH) is what you see on weather apps and home hygrometers. It measures how much moisture the air is holding compared to the maximum it could have at that temperature. For indoor spaces, you want to keep it between 40 — 60%.
- Absolute humidity measures the actual amount of water vapor in the air (in grams per cubic meter), regardless of temperature.
The key thing is that wood responds to relative humidity (RH), NOT absolute humidity. When temperature changes but absolute humidity stays the same, the RH changes. That's what causes wood to gain or lose moisture.
For example, when you heat cold winter air indoors, the absolute humidity stays the same, but the RH drops dramatically. This makes the wood dry out and shrink.
This is why wood movement happens seasonally, not day to day.
In most of North America:
- Summer: Warm + humid = higher RH = wood expanding
- Winter: Cold + dry (especially with indoor heating) = lower RH = wood contracting
2. Temperature Effects on Wood Expansion
A common question: Does wood expand in heat?
The short answer is NO. Heat alone doesn't make wood expand. Temperature by itself has almost no effect on the wood's dimensions.
But temperature matters because it's usually connected to humidity changes. Hot summer air typically holds more moisture, so your wood expands.
Heat sources like furnaces and heat vents dry out the air, which makes wood contract. Cold winter air holds less moisture, so wood contracts.
So, does wood expand in cold?
Nope. Cold winter air is usually bone dry, which means your wood shrinks to its smallest size of the year.
The real problem is furniture near heat sources. Radiators, air vents, that kind of thing. These create dry pockets that suck moisture out of the wood too fast. That's when you get excessive shrinkage and cracking.
3. Wood Movement by Species: Understanding the Differences
Different wood species move very differently from each other. And, to compare them accurately, you'll need a wood expansion chart.
But first, let us explain how you can understand these numbers about wood movement by species:
- These percentages show total shrinkage from green (freshly cut) to oven-dry wood.
- In real conditions, with a 6 — 12% moisture content, you'll actually see about 1/4 to 1/2 of these values.
- Lower numbers mean more stable wood.
- And, if the T/R Ratio is closer to 1.0, you get more uniform shrinkage, which means less warping and cupping.
*What is T/R Ratio? The T/R Ratio (Tangential-to-Radial Ratio) tells you how uniformly wood shrinks and swells.
Formula: T/R Ratio = Tangential Shrinkage ÷ Radial Shrinkage
1. Stable Woods (Minimal Movement)
Furniture and large projects are the main applications
| Wood Species | Radial | Tangential | T/R Ratio | Key Characteristics |
| Mahogany (True/Honduras) | 3.0% | 4.1% | 1.4 | Superb stability. Ideal choice for furniture and cabinetry. |
| Walnut (Black) | 5.5% | 7.8% | 1.4 | Stable and grainy wood. It’s a prime choice for high-end furniture. |
| Cherry (Black) | 3.7% | 7.1% | 1.9 | Good stability. It gets darker and more beautiful with age. Good for cabinets. |
| Teak | 2.6% | 5.3% | 2 | Highly stable and naturally rot-resistant. Premium choice for both outdoor and indoor use. |
2. Medium-Movement Woods (Moderate Stability)
Most furniture is applicable if you adopt proper joinery techniques.
| Wood Species | Radial | Tangential | T/R Ratio | Key Characteristics |
| White Oak | 5.6% | 10.5% | 1.9 | Moderate movement but excellent rot-resistance, great for outdoor furniture |
| Red Oak | 4.0% | 8.6% | 2.2 | More movement than white oak, very common and affordable |
| Ash (White) | 4.9% | 7.8% | 1.6 | Good strength-to-weight ratio, moderate stability |
3. High-Movement Woods (Requires Careful Planning)
These are beautiful woods that necessitate the use of expansion gaps and proper joinery
| Wood Species | Radial | Tangential | T/R Ratio | Key Characteristics |
| Maple (Sugar/Hard) | 4.8% | 9.9% | 2.1 | Beautiful and hard, but it moves significantly with humidity changes |
| Hickory | 7.2% | 11.0% | 1.5 | Extremely strong but high movement, best for tool handles and flooring |
| Beech (American) | 5.5% | 11.9% | 2.2 | Affordable and intense but unstable, it requires careful design. |
Note: If your desired species isn't on our wood expansion chart, find a wood with a similar Janka hardness rating and use those coefficients as an estimate.
Now that you understand how wood moves and what affects it, let's look at the actual numbers you'll use in your calculations.
Wood Expansion Chart: Quick Reference Guide
This chart shows dimensional change coefficients for common wood species. We'll use these numbers with the wood movement formula to calculate how much your project will expand or contract with seasonal humidity changes.
| Wood Species | Radial Coefficient (CR) Quarter-sawn | Tangential Coefficient (CT) Flat-sawn | Stability Rating |
| Mahogany (Honduras) | 0.00107 | 0.00146 | Excellent |
| Walnut (Black) | 0.00190 | 0.00274 | Excellent |
| Cherry (Black) | 0.00132 | 0.00254 | Excellent |
| White Oak | 0.00200 | 0.00375 | Good |
| Ash (White) | 0.00175 | 0.00279 | Good |
| Birch (Yellow) | 0.00261 | 0.00339 | Good |
| Maple (Sugar/Hard) | 0.00171 | 0.00354 | Good |
| Red Oak (Northern) | 0.00143 | 0.00369 | Fair |
| Hickory (Average) | 0.00260 | 0.00411 | Fair |
| Beech (American) | 0.00196 | 0.00425 | Fair |
| Douglas Fir (Coast) | 0.00171 | 0.00271 | Good |
| Pine, Eastern White | 0.00075 | 0.00218 | Excellent |
| Pine, Southern Yellow | 0.00182 | 0.00268 | Good |
| Cedar, Western Red | 0.00086 | 0.00179 | Excellent |
| Poplar (Yellow) | 0.00164 | 0.00293 | Good |
Wood Movement Calculator: The Formula that Solves Everything
Wood movement is not guesswork. It's mathematics. And the math is surprisingly simple.
| Movement = (Board Width) × (Species Coefficient) × (% Moisture Change) |
Now, let's break down each variable:
1. Board Width
In here, we're going to measure across the grain. That means the width of your board or panel, not the length.
This applies whether you're working with a single wide slab, multiple boards glued into a panel, a cabinet door, or a drawer side. Just measure from one edge to the other, going across the grain.
Units: Use whatever units you prefer. Inches, millimeters, centimeters, it doesn't matter. The result comes out in the same unit you put in. The coefficient works universally.
2. Species Coefficient
This is where your wood expansion chart becomes useful. You need to figure out two things.
A. Is Your Lumber Flat-sawn or Quarter-sawn?
We simply look at the end grain:
- Horizontal grain lines (arches, U-shapes) = Flat-sawn = Use Tangential Coefficient (CT)
- Vertical grain lines (perpendicular to face) = Quarter-sawn = Use Radial Coefficient (CR)
B. What Wood Species are You Working With?
Find your species on a wood movement chart and grab the right coefficient. For example, if you're building a table from quarter-sawn walnut, you'd use walnut's radial coefficient, which is 0.0019.
*What are the coefficients? These coefficients show how much the wood dimension changes for every 1% change in moisture content. They're calculated by dividing the total green-to-oven-dry shrinkage percentage by the fiber saturation point, which is about 28%.
Formula: Coefficient = (Total Shrinkage %) ÷ 28 (Fiber Saturation Point)
Simply check our wood expansion chart above to get the right specifications.
3. Moisture Change (%)
This is the difference between the highest and lowest moisture content your wood will see throughout the year. You can determine this in two ways:
Option 1: Use a Moisture Meter
- Measure your wood right now.
- Then estimate the seasonal swing. Indoors, that's usually a 2 — 4% change. Outdoors, we're looking at 6 — 8%.
- Calculate the difference between those two points.
Option 2: Use an EMC Chart (No Tools Required)
EMC charts show what moisture content wood will naturally reach based on location and season.
These charts come from 30+ years of humidity data collected by the U.S. Forest Service and NOAA. They're surprisingly accurate, often within 0.1% of what you'd get with a moisture meter.
How to use EMC charts:
- Find your city or somewhere nearby with a similar climate.
- Look up the EMC percentage for the current month.
- Then, we find the month with the biggest difference (usually summer versus winter).
- Calculate the difference between those two numbers.
| Location | Lowest EMC | Highest EMC | Annual Swing |
| Phoenix, AZ | 4.6% (June) | 9.5% (Dec) | 4.9% |
| Santa Barbara, CA | 10.7% (June) | 13.9% (Dec) | 3.2% |
| Eugene, OR | 12.7% (July) | 20.2% (Dec) | 7.5% |
| Little Rock, AR | 12.8% (Mar) | 13.9% (Sep) | 1.1% |
Note: These are outdoor EMC values. If you're working indoors with climate control, you'll typically see 50 — 75% less wood movement than what these numbers suggest.
4. Wood Movement Calculation Example
Let's build a farmhouse table, including:
- 40-inch-wide tabletop
- Quarter-sawn walnut
- Building in Santa Barbara in June
- Want to know the worst-case movement
Next, we start to calculate the wood movement:
- Step 1 (Board Width): Width = 40 inches
- Step 2 (Species Coefficient): Quarter-sawn walnut radial coefficient = 0.0019
-
Step 3 (Moisture Change): Using U.S. Forest Products Laboratory EMC data for Santa Barbara:
- June EMC = 10.7%
- December EMC = 13.9%
- Moisture change = 3.2%
We have:
(Board Width) × (Species Coefficient) × (% MC) = 40 × 0.0019 × 3.2 = 0.2432 inches
Result: About 1/4" total wood movement, or 1/8" in each direction from the center.
So, what does this mean:
For a tabletop over 3 feet wide, that's incredibly manageable. And remember, this is based on outdoor humidity data. If your furniture is indoors with climate control, it'll move way less (typically 1/4 to 1/2 of this amount)
Can You Actually Stop Wood Movement? (Or Manage It)
No, you cannot stop wood movement. Wood will always respond to moisture changes around it. That's just how the material works, and you can't change it.
But you can do 3 things.
- First, slow down how fast moisture moves in and out.
- Second, build your designs to accommodate wood movement.
- Third, pick more stable wood species and cuts.
The big mindset shift here is not to fight wood movement. Design for it.
Every professional woodworker who builds furniture that lasts for decades follows this rule. The furniture that fails is the furniture that tries to lock the wood in place.
Adapting Wood Movement Furniture: 2 Techniques that Save You from Headaches
When you've invested time and money into a beautiful wood tabletop, the last thing you want is for it to crack, warp, or pull apart from its base. Choosing the right leg attachment method and support system is essential if you want furniture that lasts.
Here are two effective solutions that work together to keep your table stable, flat, and beautiful for decades.
Method 1: Slotted Mounting Plates with Threaded Inserts
When your wood tabletop expands in summer humidity, the wood pushes outward. But regular screws are rigid and don't allow movement.
Something has to give. Usually, the wood cracks down the middle, the mounting screws break or pull out, or the metal base bends and deforms.
However, slotted mounting plates solve this problem. They have ELONGATED holes shaped like racetracks instead of round holes.
As the wood expands or contracts, the bolts slide smoothly within the slots. Your tabletop stays firmly attached to the metal table legs while moving freely.
Method 2: C-Channel Support
Even with the right leg attachment, large tabletops face another challenge: warping, cupping, and bowing.
Without support, a 6-foot dining table can cup into a U-shape across its width, bow or sag in the middle under its own weight, or twist as different sections respond to humidity changes.
That's where C-channels come in. C-channels (also called table stiffeners or support brackets) are steel bars bent into a C-shape that act like a backbone for your tabletop.
The C-shape with rolled edges provides serious rigidity to prevent sagging and bowing. The slotted holes let you secure the channel with bolts that can slide as the wood expands.
You route them into dados (channels) on the underside, so they're completely invisible from above.
Here is a quick buying guide for the number of C-channels by table length:
| Table Length | Our Recommendation | Industry Standard |
| Under 60" (5 feet) | 2 C-channels | 2 C-channels minimum |
| 60" to 96" (5 — 8 feet) | 2 C-channels | 2 C-channels |
| Over 96" (8+ feet) | 3 C-channels | 3+ C-channels |
FAQs
1. Does Wood Expand in Winter or Summer?
Wood expands in summer and contracts in winter in most climates. However, wood movement is driven by humidity changes, not temperature itself.
2. How to Account for Wood Movement?
Here's how to account for wood movement in your projects:
- Step 1: Calculate expected movement
- Step 2: Never constrain cross-grain expansion
- Step 3: Use movement-friendly joinery
- Step 4: Provide adequate clearances
- Step 5: Finish all surfaces
- Step 6: Choose appropriate wood species
3. How Much Does Wood Expand and Contract?
Here's a quick reference guide to help you estimate wood movement.
- Flat-sawn (plain-sawn) lumber: The rule of thumb is 1/4 inch per 12 inches of width. This assumes a typical 8% seasonal moisture change.
- Quarter-sawn (rift-sawn) lumber: Approximately 1/8 inch per 12 inches of width. That's about half the movement you get with flat-sawn lumber.
-
By Species (12-inch wide flat-sawn board with 8% seasonal MC change):
- Low movement woods move between 1/8" and 1/4"
- Medium movement woods move between 1/4" and 5/16"
- High movement woods move between 5/16" and 3/8"
For precise calculations: If you need exact numbers, you can use a wood movement calculator in our guide or the formula with your specific wood species coefficient (from a wood expansion chart), board width, and expected moisture change in your location.
4. Do Screws Allow for Wood Movement?
Sadly, standard screws do NOT allow for wood movement. A regular screw driven through one board into another creates a rigid connection that stops movement completely.
But that doesn't mean we can't accommodate wood movement. Here are 3 proven methods to do that:
- Slotted holes and washers
- Purpose-built fasteners
- Oversized counterbores
Building Wood Movement that Lasts Generations: Conclusion
After reading this guide, we hope you understand one thing. Wood movement is predictable, measurable, and manageable.
It's not the mysterious disaster that people online make it sound like. It's not something to be scared of. It's just a property of wood that you need to work with in your designs.
Furniture builders who get this can create pieces that last 50, 100, or even over 200 years. Look at the antiques in museums and old homes today.
Those weren't built with modern moisture meters or wood movement calculators. They were built by craftspeople who understood these principles and designed around them.
Also, we share new blogs every week, so check back if you found this helpful. And, if you have questions about wood movement or need help finding the right table legs for your project, we're here to help at Flowyline. Thank you!
