Methodology

Framing mistakes are expensive because they are discovered late. A rafter cut long is found when the pair will not close at the ridge. A hip cut on a twelve inch unit run is found when it will not reach the corner. A deck board count short by nine percent is found with two rows left to lay and the supplier closed. In each case the arithmetic looked right and something outside it was missed.

Every result names its source

Each calculator lists the formula, standard or code section behind it, and each result row states which one produced that specific number. Where a figure comes from a published standard — IRC R806.2, IRC R905.2, the USDA Wood Handbook — it is cited by section rather than described vaguely. Across this site that is 35 distinct cited sources.

This is not decoration. A hip rafter result that says “16.97 inch unit run, +0.333 inch against the 17 inch field shortcut” tells you what the number is and how far the rule of thumb would have put you out. One that returns a length and nothing else lets you cut an expensive timber before discovering which convention it used.

Calculations are code, and code is tested

Every calculator is a small program with an automated test suite that runs before anything is published, and the tests do more than confirm the arithmetic. A subset of them assert the specific behaviour that makes each tool worth using: that a deck board is five and a half inches wide rather than six, that a hip rafter runs 16.97 inches for every twelve a common rafter runs, that a beam picks up half the span on each side and not the whole of it.

Those assertions are deliberately brittle. If a change to an assumption breaks one, what changed is not a number but what the tool claims. That is the point of writing them that way.

Published data is checked against its own definition

Some reference values are not looked up at all — they are defined, and can be recalculated from first principles. Wire gauges follow a geometric standard, circular mils are a definition, conduit areas are a circle, nominal lumber sizes follow a documented rule, and a sheet area is a multiplication. Every value of that kind on this site is verified against its own definition by an automated check, not transcribed and hoped over.

One source of truth

Reference data lives in one place and feeds both the calculators and the published charts. The roof pitch chart, the rafter calculator and the roofing material calculator all derive the slope factor from one formula, so three pages cannot disagree about the area of the same roof. Two pages on this site cannot give different answers for the same question, because there is only one answer in the code.

What these tools do not do

Every calculator carries a disclaimer naming what it does not model, and those are worth reading. Structural pages give geometry and load, not engineered designs or member sizes. Wood movement coefficients are published averages and vary within a species as much as between them.

Building and electrical codes also vary by jurisdiction and change between editions. Local amendments are frequently stricter than the model codes these tools reference, and your authority having jurisdiction decides what is acceptable where you are.

Independent review

The calculations here are compiled from published standards and established engineering practice, and are checked by the automated test suite described above. They have not been reviewed by an independent licensed professional.

That is the reason tools whose output would be safety-critical if it were wrong are not published on this site. Conductor and overcurrent sizing, structural spans and bearing, stairs and guards, and roof snow loading all depend on code tables where a single wrong cell produces a confident and dangerous answer — and a table that is wrong in a consistent way passes every test that can be written for it. Those tools are held back until their tables have been checked against a verified current code copy.

What is published is geometry, material takeoff, and sizing that works from figures you read off your own equipment. Verify anything you intend to build, wire, or rely on against your current code book or a licensed professional.

Corrections

We would rather be corrected than be wrong. If you can point at the table or code section we have misapplied, write to hello@framingcalcs.com with the inputs you used, the result you got and the result you expected. Reports that identify a specific source get tested against, and fixed.

We do not answer project-specific technical questions or review plans. See the contact page for what we can and cannot help with.