Concrete Calculator
How many cubic yards of concrete for a slab? Enter length, width and thickness and get cubic feet, cubic yards and tons — with the waste allowance ready-mix jobs need.
4 in for a patio or walkway, 6 in for a driveway.
10% covers spillage, uneven subgrade and form overfill.
Concrete for a 100 sq ft slab, 4 in thick
1.36 cu yd — 36.7 cu ft · 1.04 cu m · about 2.7 tons
Exact volume is 33.3 cu ft (0.94 cu m); with 10% waste, order 1.36 cu yd. Ready-mix is sold by the cubic yard (27 cu ft), and most suppliers have a minimum order of 1 cu yd plus a short-load fee under about 3–4 cu yd — for very small pours, bagged mix is usually cheaper.
Estimate. Measure the forms after they are set — a form that is an inch deeper than planned adds a surprising amount of concrete. Confirm the price per yard with the plant; it varies by mix, region and delivery distance.
Formula used: Volume = length × width × (thickness ÷ 12) cubic feet, × (1 + waste%). Cubic yards = cubic feet ÷ 27.
How this estimate works: Concrete volume is length times width times thickness, converted from inches to feet. Ready-mix plants sell by the cubic yard, so the tool divides by 27 — and adds a waste allowance first, because forms are rarely perfectly level and a little concrete always spills. One cubic yard of concrete weighs about 2 tons, which matters if you are hauling it yourself.
How the concrete calculator works
Concrete volume is length times width times thickness, converted from inches to feet. Ready-mix plants sell by the cubic yard, so the tool divides by 27 — and adds a waste allowance first, because forms are rarely perfectly level and a little concrete always spills. One cubic yard of concrete weighs about 2 tons. Most suppliers have a minimum order of 1 cu yd plus a short-load fee under about 3–4 cu yd, so for very small pours bagged mix is usually cheaper.
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