Almost every material question — concrete, mulch, tile, paint, sod — comes down to one of three measurements: area, volume, or coverage. Get comfortable with these and you can estimate anything.
1. Area (for flat things)
Area is length × width, measured in square feet. It answers "how much surface am I covering?" — flooring, tile, paint, sod, drywall. For a circle, area is π × radius². For odd shapes, split them into rectangles, measure each, and add them up.
Example: a 12 ft × 10 ft room is 120 ft². That's the number you feed into the tile calculator or flooring calculator.
2. Volume (for things with depth)
Volume is area × depth, and bulk materials are sold by the cubic yard (27 cubic feet). Concrete, gravel, mulch and soil are all volume problems. The classic mistake is mixing units — your depth is usually in inches, so convert it to feet (divide by 12) before multiplying.
Example: a 10 × 10 ft patio at 4 inches of gravel is 100 ft² × 0.33 ft = 33 ft³ ≈ 1.2 cubic yards. The gravel calculator and concrete calculator do this conversion for you.
3. Coverage (when one unit covers a known amount)
Coverage flips the problem around: one bag, box, gallon or roll covers a set amount, so you divide your area or volume by that figure. A gallon of paint covers ~350 ft²; a 2 ft³ bag of mulch covers ~12 ft² at 2 inches deep.
Example: 666 ft² of wall ÷ 350 ft² per gallon ≈ 2 gallons of paint. That's exactly what the paint calculator computes.
Always add waste
Real projects aren't perfect. Add 10% for most jobs — cuts, spillage, uneven ground, breakage — and up to 15% for diagonal tile or patterned materials. Running out mid-job costs far more than a little overage.
Let the calculators do the math
Every calculator on this site has the conversions and a waste allowance built in. Measure carefully, type the numbers in, and buy with confidence.