Quick Math
Fraction-accurate dimensional math and one-tap job-site conversions.
Dimensional Calculator
+ and − give a length · × gives an area · ÷ gives a count. Results round to the nearest 1/16".
Quick Conversions
1 acre = 43,560 sq ft
Tools for this job
SponsoredGear we'd reach for on this job. As an Amazon Associate, BuildCalc earns from qualifying purchases — at no extra cost to you.
How the construction math calculator works
Quick Math is a dimensional calculator built for the job site. It adds, subtracts, multiplies and divides measurements in feet, inches and fractions — so you can work out 12' 4" minus 3-5/8" without converting to decimals in your head. Results round to the nearest 1/16 inch.
Plus and minus return a length. Multiply two lengths for an area. Divide one length by another for a count — handy for finding how many joist bays fit in a span. The conversions panel handles fast, everyday swaps: square feet to acres, cubic feet to cubic yards, millimeters to inches, and roof pitch to degrees.
Guides
- How many cubic feet in a cubic yard? — the 27 cu ft conversion with worked examples for concrete, mulch and gravel.
- How many square feet in an acre? — the 43,560 conversion with lot-size examples.
Construction math FAQ
How do I add feet and inches?+
Enter each measurement as whole feet, whole inches and a fraction, then choose the plus operator. Quick Math converts everything to a common unit internally and returns a clean feet-inches-fraction result, rounded to the nearest 1/16 inch.
How do I convert roof pitch to degrees?+
Roof pitch is written as rise over 12 inches of run — a 6/12 pitch rises 6 inches per foot. The angle in degrees is the arctangent of the rise divided by 12. A 6/12 pitch is about 26.6 degrees; the conversions panel does it instantly, either direction.
How many square feet are in an acre?+
One acre is 43,560 square feet. The conversions panel converts either direction — square feet to acres or acres to square feet.
How do I figure out joist bays in a span?+
Divide the total span by the joist spacing using the divide operator. A 10-foot span divided by 16 inches gives 7.5 — so the span holds seven full bays. The count rounds down to whole bays.
How do I convert inches to millimeters?+
One inch equals exactly 25.4 millimeters. The conversions panel converts inches to millimeters and back.
How many cubic feet are in a cubic yard?+
There are 27 cubic feet in a cubic yard. Use the cubic feet to cubic yards conversion to switch between them when ordering material.