Foundation Squaring Calculator

Get the corners right before you pour.

Enter your length and width and the app gives you the diagonal a square layout has to measure — in feet and inches to the nearest 1/16", or in meters. Pull both corner-to-corner measurements, type them in, and it tells you whether you're square and exactly how far to move a corner if you aren't.

What it does

• Required diagonal — the measurement both corner-to-corner pulls must match, shown as a tape reading and a decimal, plus perimeter for your string line and enclosed area.
• Off-square fix — enter the two diagonals you actually measured and get a straight answer: which one is long, and how far to draw a corner in to bring the layout square. Move one corner, or split it between both ends.
• L-shaped footprints — describe the overall size and the cut-out corner; the app splits it into two rectangles, gives a diagonal for each, and confirms the inside corner. Rotate the drawing to match what's staked on the ground.
• Your tolerance — decide what counts as square: 1/16", 1/8", 1/4", 1/2", or 1–12 mm. Tight formwork and a garage pad don't need the same standard.

Built for the job site

• Feet-and-inches entry with real fractions — type 1 11/16, or 11/16, or 1.5
• Round results to 1/8", 1/16", or 1/32" to match the tape in your pocket
• Full metric mode
• Scale drawings that show which way the layout leans and which diagonal to pull
• Large, high-contrast numbers; light and dark themes
• Your measurements are still there when you come back to the phone
• Works with no signal — every calculation runs on the phone
• In English and Spanish

Who it's for

Concrete and foundation crews, framers, deck and shed builders, fence and post-hole layout, landscapers setting patios and pads, and anyone who has ever pulled a diagonal twice and gotten two different numbers.

The math

A rectangle is square when both diagonals equal the square root of length squared plus width squared — the 3-4-5 rule, generalized to any size. When the diagonals disagree, the layout has racked into a parallelogram, and the exact correction is the long diagonal minus that target.

Layout guidance only. Always confirm critical dimensions against the stamped drawings and your local code before you pour.