Builderology publishes 59 free construction and woodworking calculators and a wood species database of 192 woods. This page explains where their numbers come from, how we check them, and what they are not meant for.
Where the numbers come from
Every calculator and data page lists its sources at the bottom, and the formula it uses in a “How it works” section, so you can check the arithmetic yourself. We use published references rather than rules of thumb wherever one exists:
| Source | Used for | Notes |
|---|---|---|
| USDA Forest Products Laboratory, Wood Handbook (FPL-GTR-190) | Wood species properties, shrinkage and movement, density and weight, equilibrium moisture content | Public domain (US Government) |
| Industry associations (NCMA, BIA, American Wood Council) | Block and brick counts per square foot, mortar, deck footing sizes | Cited on each calculator page |
| ASTM and ASME standards | Rebar weights, nail sizes, thread and drill sizes | Cited on each calculator page |
| International Residential Code (IRC) | Stair, rafter and deck rules of thumb used as planning references | Cited; confirm with your local code |
| Manufacturer data sheets | Coverage rates such as glue, joint compound and shingles | Cited on each calculator page; brand names kept out of titles |
Wood data comes straight from the tables of the USDA Wood Handbook. We read the tables into a data file with a script, checked sample values by hand against the printed tables, and generate every species page and chart from that one file, so a number is the same wherever it appears. Where a value is our estimate rather than a tabulated figure, the page marks it and shows the Handbook equation used.
How the calculators are tested
- Known-answer tests. The calculation code has 136 automated tests. Where a source publishes a worked figure (for example NCMA’s 119 blocks per 100 sq ft, BIA’s 675 modular bricks per 100 sq ft, or the Wood Handbook’s equilibrium moisture content table), the test checks the calculator against it.
- Nothing is published if a test fails. The build that creates the pages runs the tests first and stops on any failure.
- Browser checks. Each calculator is loaded in a headless browser on a phone-sized screen to confirm it renders, responds to changed inputs, shows an error line for bad input and does not overflow the screen.
- Worked example results are generated. The inputs and results listed in each worked example are produced by the same code that runs the calculator.
Corrections
When we find a mistake we fix it on the page, keep the same address and update the “Last reviewed” date shown at the bottom of the page. For example, in October 2026 we changed the rebar calculator to round the number of bars up, so the actual spacing is never wider than the spacing you enter, and corrected the shrinkage values for several imported woods in the wood movement calculator to the Wood Handbook figures. If you spot an error, please tell us.
What these tools are not
- They are planning and estimating tools. They do not replace plans, a building permit, an engineer or a licensed contractor.
- Structural and safety-related results (footings, spans, stairs, rebar) are estimates. Check them with your local building department or a licensed professional before you build.
- Wood property values are averages for small, clear test specimens. Real boards vary, and graded structural lumber uses separate design values.
Where to start
- All construction and woodworking calculators
- Wood species database and Janka hardness chart
- About Builderology
Last reviewed: 22 October 2026.