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 (14' 1 11/16") and as 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 diagonal is long, and how far to draw a corner in to bring the layout square. Move one corner the full amount, or split it between both ends. No guessing, no trial and error.

• L-SHAPED FOOTPRINTS — describe the overall size and the cut-out corner. The app splits the footprint into two rectangles and gives you a diagonal for each, plus a confirmation shot to the inside corner so you know the notch landed right. 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, so a basement or a rural lot is fine
• 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.

SUBSCRIPTION

A seven-day free trial opens everything. After that it's $1.99 a month or $9.99 a year, or a one-time $24.99 for lifetime access with nothing to renew. Prices are in US dollars and vary by country.

Subscriptions renew automatically until cancelled. Cancel any time in the Play Store — cancelling keeps your access until the period you've paid for ends.

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. For small errors this comes out to the familiar "half the difference" rule of thumb, but it stays correct when a layout is badly out.

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