Supply MathAbout Supply Math
Supply Math answers one question before every home or yard project: how much do I need to buy? Concrete, gravel, mulch, topsoil, square footage: enter your measurements in feet and inches and get cubic yards, tons and bag counts you can take straight to the store or a supplier.
Supply Math is an independent website. It isn’t owned by a manufacturer or retailer, and no brand pays to change the results.
What we promise
- Fast and free. No sign-up, nothing to install. The calculators run in your browser, and the numbers you type are never sent to us.
- Show the math. Every calculator page explains the formula and the assumptions, so you can check it yourself.
- Round up, not down. Bag counts are rounded up and include an adjustable waste margin, because running short mid-pour costs more than a spare bag.
- Clean ads. When the site shows ads, they’ll stay out of the way: no pop-ups, and never inside the calculators.
Where our numbers come from
- Concrete bag yields: manufacturer data (Quikrete Concrete Mix No. 1101 data sheet): 80 lb ≈ 0.6 ft³, 60 lb ≈ 0.45 ft³, 40 lb ≈ 0.3 ft³.
- Bags per pallet: manufacturer product pages: 42 × 80 lb, 56 × 60 lb.
- Gravel, sand and stone: typical bulk weights of 1.35–1.6 tons per cubic yard. Because stone size and moisture change the weight, our gravel calculator lets you type in your supplier’s own figure.
- Ready-mix trucks: a standard truck carries up to about 10 cubic yards.
- Unit conversions: exact: 27 ft³ per cubic yard, 9 sq ft per square yard, 43,560 sq ft per acre, 10.764 sq ft per square meter.
All results are estimates for planning and ordering. Real projects vary (uneven ground, form bowing, compaction, spillage), so confirm quantities with your supplier, and follow local building codes and a qualified professional for structural work.
Corrections
If a result looks wrong, tell us the page and the numbers you used: hello [at] supplymath.com. We check every report and fix confirmed errors quickly. Every calculator is backed by automated tests of its math.