Square-Up Calculator
Enter length and width and get the diagonal that makes the frame square. Measured yours? It tells you how far out you are and which way to rack. Plus a 3-4-5 marker for laying out corners with nothing but a tape.
No framing square handy? Mark a right angle with a tape.
Planning tool — results are estimates for quoting and ordering, not engineering or building-code advice.
Common questions
How do I square a deck frame with the diagonal?
Measure both diagonals corner to corner. When they match the target this calculator gives you (and each other), the frame is square. If one is long, rack the frame toward the long diagonal's corners until they equalize.
What is the 3-4-5 method?
A triangle with sides in a 3:4:5 ratio always contains a perfect right angle. Mark 3 units along one line and 4 along the other; when the diagonal between the marks is exactly 5 units, the corner is square. The calculator scales the ratio to any size, like 6' : 8' : 10'.
How close is "square enough"?
The verdict allows 1/4" by default — fine for decks and framing. Tile and cabinetry want tighter; treat the delta readout as the real answer.
Related: Stairkey for remodeling · Spacing calculator
More free calculators
All 14 are free, feet-and-inches in, no sign-up. Pick the next one for the job.
Concrete & site work
Finishes & materials
Layout & geometry
This solves one measurement. The Takeoff Builder prices the whole job.
Walk the rooms, enter dimensions, and formula-driven scope turns measurements into quantities, prices, and the estimate itself — from $20/mo, capped, no surprise bills.