Estimate the volume and weight of concrete for a slab, wall, hole, column, circular slab or tube, curb and gutter, or stairs. Enter lengths in feet, inches, yards, metres, or centimetres. Results include cubic feet, cubic yards, cubic metres, pounds, kilograms, and 60 lb / 80 lb bag counts. Buying slightly more than the estimate reduces the chance of running short.
Formula
All lengths convert to feet (1 m = 1 / 0.3048 ft). Volume of one shape is multiplied by quantity (stairs have no quantity — use the riser count instead).
V_ft³ = shape volume × quantity
V_yd³ = V_ft³ / 27
V_m³ = V_ft³ × 0.028316846592
weight_lb = V_ft³ × 133
weight_kg = V_m³ × 2130
bags_60 = weight_lb / 60
bags_80 = weight_lb / 80
Shape volumes in feet:
slab / wall / footing V = L × W × H
hole / column V = π (d / 2)² H
tube / circular slab V = π ((d1 / 2)² − (d2 / 2)²) H
curb & gutter V = L × (curbDepth × (curbHeight + flagThickness)
+ gutterWidth × flagThickness)
Stairs use inches (12 in = 1 ft), n risers, and n − 1 treads:
V_ft³ = Width × (Run × Rise × Treads × (Treads + 1) / 2
+ PlatformDepth × Rise × Risers) / 1728
Density and bags
Pre-mixed bagged concrete on this page uses 133 lb/ft³ (2,130 kg/m³). Cubic metres are (0.3048)³ = 0.028316846592 times cubic feet.
| Input | Result |
|---|---|
| 1 ft³ | 133 lb, 0.037 yd³, 0.0283 m³ |
| 1 yd³ | 27 ft³, about 3,591 lb |
| 60 lb bag | weight / 60 |
| 80 lb bag | weight / 80 |
Concrete is coarse aggregate (sand, gravel, crushed stone) bonded with cement, most often Portland cement. It is sold in 60 or 80 lb bags or delivered by mixer truck. Mixing is time-sensitive: place the mix before it hardens. Curing takes about four weeks to reach over 90% of final strength and can continue for years; keeping the surface damp in the early days improves strength.
Examples
5 ft by 2.5 ft slab, 5 in thick
Volume is 5 × 2.5 × 5/12 = 5.21 ft³ (0.19 yd³, 0.15 m³), 692.71 lbs / 314.14 kg, or about 11.55 60 lb bags / 8.66 80 lb bags.
2.5 ft diameter hole, 6 ft deep
A cylinder of radius 1.25 ft is 29.45 ft³ (1.09 yd³, 0.83 m³), 3,917.17 lbs / 1,776.42 kg, 65.29 / 48.96 bags.
Tube 5 ft outer, 4 ft inner, 6 in tall
Annulus volume is 3.53 ft³ (0.13 yd³, 0.1 m³). Equal diameters give 0; an inner diameter larger than the outer gives no result.
Curb and gutter, 10 ft run
Curb depth 4 in, gutter width 10 in, curb height 4 in, flag 5 in, length 10 ft is 5.97 ft³ (0.22 yd³, 0.17 m³).
Five-riser stairs
Run 12 in, rise 6 in, width 50 in, platform 5 in, 5 risers (4 treads) is 25.17 ft³ (0.93 yd³, 0.71 m³), 3,348.09 lbs, 55.8 60 lb bags.