How to Calculate Concrete Yards (Quick Reference)
A pocket reference card for calculating concrete yards. Five formulas, one conversion table, no fluff.
Five formulas and one conversion factor cover almost every residential pour. Bookmark this page, screenshot the infographic, do the math.
The conversion
Cubic feet ÷ 27 = cubic yards. That's the only number you really have to remember. Everything else is the volume formula for whatever shape you're pouring. If you'd rather multiply: cubic feet × 0.037 = cubic yards.
Slab math in one line
For a slab, the rule of thumb is: length-feet × width-feet × thickness-inches ÷ 324 = cubic yards. That bakes the inch-to-foot conversion (×1/12) and the divide-by-27 into a single divisor of 324. It's the fastest mental math for sizing a patio.
Examples: a 10 × 10 × 4 patio is 10 × 10 × 4 ÷ 324 = 1.23 yd³. A 20 × 20 × 4 driveway is 1,600 ÷ 324 = 4.94 yd³. A 60 × 4 × 4 sidewalk is 960 ÷ 324 = 2.96 yd³.
Round-footing math in one line
For a round footing: diameter-inches² × depth-feet × 0.0021 = cubic yards. That's π/4 × (1/144) × (1/27) collapsed. Useful for sizing 12-in or 16-in piers without breaking out a calculator.
Example: a 12-in diameter × 4-ft pier is 144 × 4 × 0.0021 = 1.21 ft³ ≈ 0.045 yd³ per pier. Multiply by your pier count and you have the deck-foundation total.
Tube math in one line
For a hollow tube (pipe, planter, ring): (d₁² − d₂²) × length-feet × 0.0021 = cubic yards where both diameters are in inches. The d₁² − d₂² subtraction handles the wall area.
Stair math by hand
Stairs don't reduce as cleanly because the wedge under each tread accumulates. The shortcut: total volume ≈ ½ × N × rise-inches × run-inches × width-inches ÷ 1,728 (cubic feet) ÷ 27 (cubic yards), where N is the number of steps. Add the platform separately if there is one. For most residential stoops with 4–6 steps, the total comes out to 0.4–0.7 cubic yards.
The 7-yard rule
Below 7 yd³, residential ready-mix is almost always cheaper than bagging it yourself when you account for labor. Below 1 yd³, bags usually win. Between 1 and 7 yards, compare local pricing — bag prices vary wildly between regions and the math flips.
Density at a glance
One cubic yard of standard-weight concrete weighs 4,050 lb (1,840 kg). So if your math gives you 3 yd³ but you're pricing trucking and hand-loading, that's six tons of concrete. The density used in this calculator is 2,130 kg/m³ (133 lb/ft³), which is a typical mid-range value for normal-weight concrete with standard gravel aggregate.
For anything more complex than rough mental math — multiple shapes, mixed units, or just to double-check your phone math — use the volume calculator.
Frequently asked questions
How much does a yard of concrete weigh?
About 4,050 lbs (1,840 kg) for standard normal-weight concrete at 133 lb/ft³ density. That means six tons for a 3-yard pour — worth knowing if you're hand-loading wheelbarrows or sizing a delivery truck for a steep driveway.
How many bags of concrete do I need?
Multiply your cubic yards by 45 for 80-lb bags, 60 for 60-lb bags, or 90 for 40-lb bags. So a 1-yard pour is 45 of the 80-lb bags. For under 1 yard, bags are usually cheaper than ready-mix; above 1 yard, ready-mix wins on price and labor.