Estimate wood shrinkage with this process:

1. Determine Moisture Content (MC): You need the wood's initial MC (when you get it) and the expected final MC (the environment where the project will live). A moisture meter is the best tool for this.
2. Select Wood Species: Choose your wood from the list. Different species shrink at different rates.
3. Identify Grain Orientation: Is your board flatsawn or quartersawn? This significantly impacts the direction and amount of shrinkage. Width shrinkage is primarily tangential, and thickness shrinkage is radial.
4. Enter Initial Dimensions: Measure the width and thickness of your board at its initial moisture content.
5. Calculate: The calculator applies the shrinkage formula to predict the final dimensions.

• Moisture Content (MC): The weight of water in a piece of wood, expressed as a percentage of the wood's oven-dry weight.
• Fiber Saturation Point (FSP): The MC level at which wood's cell walls are fully saturated, but no free water exists in the cell cavities. Shrinkage starts when the MC drops below the FSP, which is typically around 28-30%.
• Tangential Shrinkage: Shrinkage that occurs parallel to the growth rings. This is the largest amount of shrinkage.
• Radial Shrinkage: Shrinkage that occurs perpendicular to the growth rings. It is typically about half of the tangential shrinkage.
• Flatsawn (Plainsawn): Lumber cut so that the growth rings are relatively parallel to the wide face of the board. It is most prone to tangential shrinkage across its width.
• Quartersawn: Lumber cut so that the growth rings are perpendicular to the wide face. It is more stable, with radial shrinkage occurring across its width.

"The numbers from any shrinkage calculator are an excellent guide, but they are still estimates. Real-world wood can have internal stresses, unusual grain, and variations from the book values. Always allow a little extra room for movement in your joinery, especially for wide, flatsawn panels. That's what techniques like breadboard ends and frame-and-panel construction are for." - Master Cabinetmaker

"Acclimation is key. Before you start a project, let your wood sit in your shop for several weeks to reach Equilibrium Moisture Content (EMC) with its new environment. This minimizes a lot of the post-construction movement you might otherwise fight."

Example 1: A Wide Tabletop
You are building a tabletop from a single, 18-inch wide flatsawn Red Oak board. Its current MC is 15% (air-dried), and it will live in a home with an average MC of 8%.
MC Change: 15% - 8% = 7%. Red Oak Tangential Shrinkage: 8.6%.
Width Change: `18" * (8.6 / 100) * (7 / 30) ≈ 0.36"`
The 18" board will shrink by over 1/3 of an inch. You must use joinery that allows for this movement.

Example 2: Quartersawn Fir Flooring
You're installing 3-inch wide quartersawn Douglas Fir flooring. It arrives at 12% MC and will acclimate to 7% MC.
MC Change: 12% - 7% = 5%. Douglas Fir Radial Shrinkage: 4.8%.
Width Change per board: `3" * (4.8 / 100) * (5 / 30) ≈ 0.024"`
While small per board, over a 15-foot wide room (180 inches / 3 inches/board = 60 boards), the total shrinkage will be `60 * 0.024" ≈ 1.44"`. This is why leaving an expansion gap along the walls is critical.

• Ignoring Grain Direction: Mixing up tangential and radial shrinkage is a common error. The orientation of the growth rings determines the direction of maximum shrinkage.
• Assuming All Wood is the Same: Different species shrink by vastly different amounts. A piece of Hickory will move much more than a piece of Teak of the same size.
• Calculating for Swelling: This calculator is designed for shrinkage (drying). While swelling (gaining moisture) uses the same principles, it's less common in project building to go from a dry state to a permanently wet one.
• Forgetting about Length: Longitudinal (lengthwise) shrinkage is so minimal (typically 0.1% to 0.2%) that it is considered negligible in most woodworking applications.

• Panel Glue-Ups: Predicting the total shrinkage of a wide panel to inform joinery choices.
• Furniture Design: Designing case work, drawers, and doors that will not bind or split as seasons change.
• Flooring Installation: Calculating the necessary expansion gap to prevent buckling.
• Lumber Purchasing: Buying green or air-dried lumber and knowing how much usable width will remain after drying.