Free construction calculators: check the maths before you cut
A wrong count costs a second trip to the yard. Type what you measured and get the buy list for decks, stairs, roofs, rafters, railings, pavers, drainage and squaring, plus a feet and inches calculator for the fraction maths. Formulas shown, code sections named.
- Formulas shown
- Code sections cited
- No account, no cookies
Pick the job
Deck material
Boards, joists, beams, posts and a cost you can edit.
Try it →02Stair & stringer
Total rise in; risers, treads, stringers and an IRC check out.
Try it →03Baluster
Count, equal gap and on-centre spacing, checked against the 4 in ball.
Try it →04Roof pitch
Rise and run in; x:12 pitch, degrees, slope and multiplier out.
Try it →05Roof area
Building size and pitch in; roof area, squares and bundles out.
Try it →06Rafter
Span and pitch in; rafter length, birdsmouth and hip length out.
Try it →07Paver
Pavers, base, sand and cost for patios, circles and fire pit rings.
Try it →08French drain
Gravel, pipe, fabric, slope and a cost you can edit.
Try it →09Squaring
Two sides in; the diagonal that squares a layout out.
Try it →10Feet & inches
Add, subtract, multiply and divide tape-measure lengths. Decimals and mm too.
Try it →How it works
- Pick the job. Each calculator does one thing, like the boards for a deck or the risers for a stair, so there is nothing to learn first.
- Type what you measured. Write it the way you read it: 5' 3 1/2", 63.5 or 1.6m all work, and the units follow your browser unless you change them.
- Check it, then copy it. The result shows its working and its code check. Copy the list into a message or a materials order.
Built to be checked
Every formula is printed on the page. The worked examples run on the same code as the calculator, and each code check names its section, so you can read the source instead of taking our word. No account, no ad network, no cookie.
These are planning estimates. They do not replace drawings, engineering or the code enforced where you build.