Mark the dimension before selecting the direction
Draw the part as it will be installed, with its part ID and grain arrow. Highlight the distance being entered as width. For a tabletop, that may be the distance across the boards; for a panel in an opening, it is the dimension between the relevant constraints. Record the current measured width rather than a nominal stock label or an old drawing value. If the dimension runs along the fibers, this cross-grain calculator is the wrong model. The planner does not turn a two-dimensional cut list into a complete three-dimensional deformation analysis.
Read the end grain with the drawing beside it
The radial direction runs outward from the center of the tree; the tangential direction follows its growth rings. A quartersawn width is modeled radially and a flatsawn width tangentially. Those labels describe idealized directions. Use an accessible end-grain view to check how the rings sit relative to your marked dimension, and photograph or sketch the evidence with the part ID. A decorative face pattern alone is a weak record for a later reviewer who cannot see the same end. The USDA structure chapter supplies the anatomical reference; your sketch connects it to this particular part.
Use the comparison when the direction remains uncertain
Choose “Compare both directions” to see separate radial and tangential calculations using identical project inputs. Keep both results visible in the review rather than averaging them into an apparently precise answer. This tool does not calculate a ring-angle interpolation, assign probabilities or validate a mixed-board glue-up. For a panel assembled from stock with different directions, record the individual boards and review the construction separately. A small result in one scenario is not evidence that the actual panel will follow it. Resolve the orientation and construction assumptions before making a fit-critical decision.
Match the exact species entry
The coefficient list names eight entries transcribed from the 2021 Wood Handbook table, including “Red oak (northern red)” and “White oak (white).” Retain the specific supplier identification in your notes. Do not select the nearest familiar name solely because it gives a convenient result. If the stock cannot be matched to a listed entry, obtain a suitable species reference and method rather than relabeling it. The Wood Species Library is useful for broader material discovery; this planner owns a narrower question about a documented dimension under an entered moisture scenario.
Keep the coefficient and percentage-point change together
The estimate follows Equation 13–3: dimension change = measured width × directional coefficient × change in wood moisture content. Moisture values are entered as percentages, so a move from 8% to 12% is four percentage points. Do not enter 0.08 and 0.12 into the form. The source table coefficients are referenced to a 10% MC dimension and the handbook uses them as an approximation with the starting measured dimension. Exports retain the coefficient, current reading, endpoints and method so another person can reproduce your calculation.
Audit the example without changing the other inputs
Load the white oak tabletop example and leave width and moisture inputs unchanged. Switch between tangential and radial models. Review the seasonal change, expansion from the current reading and remaining opening space as three different outputs. The change in the result should come only from the coefficient. Next, double the width and check how the predicted displacement changes. This is a useful way to understand the model before entering your own dimensions. Reset by loading the example again; examples replace the current working draft, so export a backup first if you want to keep it.
Record what the estimate leaves unresolved
Keep the chosen direction and the evidence beside the project label. Note any mismatch between supplier description, drawing and physical stock. Record the actual opening independently; do not adjust it to hide a larger modeled movement. Check whether a finish, edging, attachment or neighboring component changes the physical detail being reviewed. Plywood, MDF, along-grain movement, cupping and restrained stresses are outside this calculator. Move to the appropriate material or construction method when the part does not match the model. The next guide covers how to make the moisture inputs equally reviewable.
Sources and method boundary
USDA Wood Handbook, Chapter 13 (2021) — Table 13–5, page 13–17, supplies the coefficients; Equation 13–3, page 13–16, supplies the approximation used by the planner. Checked 2026-10-11.
USDA Wood Handbook, Chapter 3 (2021) — Planes of section and the appearance of sawn lumber provide the anatomical basis for reading radial and tangential directions. Checked 2026-10-11.