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.
Density and bags
The weight estimate uses 133 lb/ft³. Bag estimates use the approximate packaged-product yields below, independently of that weight assumption. 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 | approximately 0.45 ft³ yield |
| 80 lb bag | approximately 0.60 ft³ yield |
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 conditions matter as much as the volume estimate: follow the chosen mix's instructions for moisture, temperature, and curing time.
Slab planning worksheet: 10 ft × 6 ft × 4 in
This is a checkable starting estimate for a small rectangular slab. Measure the formed inside dimensions and the planned average thickness; do not use the outside dimensions of the forms.
| Step | Calculation | Estimate |
|---|---|---|
| Convert thickness | 4 in ÷ 12 | 0.333 ft |
| Find volume | 10 ft × 6 ft × (4/12) ft | 20 ft³ |
| Convert for ready-mix | 20 ÷ 27 | 0.74 yd³ |
| Estimate 60 lb bags on this calculator | ceil(20 ÷ 0.45) | 45 bags |
| Estimate 80 lb bags on this calculator | ceil(20 ÷ 0.60) | 34 bags |
Check the product yield before buying. The QUIKRETE Concrete Mix data sheet lists approximately 0.45 ft³ per 60 lb bag and 0.60 ft³ per 80 lb bag. On those label yields, 20 ÷ 0.45 rounds up to 45 bags, and 20 ÷ 0.60 rounds up to 34 bags. The calculator uses those yields directly, but another mix can yield differently. Neither count includes extra for uneven ground, spillage, or form overfill. Confirm thickness and any structural requirements with the project plan before ordering.
That same product sheet recommends maintaining suitable curing conditions for at least 5 days in warm weather or 7 days in cooler weather. This is product guidance, not a universal structural specification; use the actual mix's instructions and local project requirements.
The calculator's 133 lb/ft³ is an estimating assumption, not a universal bag yield or wet-concrete density. Use the selected product's stated yield for a purchase decision; use cubic yards and the supplier's ordering guidance for ready-mix.
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 / 314.21 kg, or about 11.57 60 lb bags / 8.68 80 lb bags. The whole-bag purchase counts are 12 and 9 before any added project allowance.
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 / 1,776.8 kg, 65.45 / 49.09 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, about 55.94 60 lb bags, or 56 whole bags before any added project allowance.
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 = weight_lb × 0.45359237
bags_60 = V_ft³ / 0.45
bags_80 = V_ft³ / 0.60
purchase bags = ceil(estimated bags)
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
Limits of the estimate
This calculator finds geometric volume and a planning quantity. It does not determine slab thickness, footing dimensions, concrete strength, reinforcement, joints, subgrade preparation, curing method, or code compliance. Uneven excavation, form movement, spillage, and product yield can change the amount needed. Use the project drawings or qualified local guidance for structural requirements, and confirm ready-mix order increments or bag yield with the supplier before purchase.
Waste and multiple pours
The optional purchasing section adds a waste percentage to the combined net
volume. The current shape already includes its Quantity value. Add other pours
as one line each: Patio, 2, yd3 or Footings, 0.5, m3. Use ft3, yd3 or m3.
Calculate other shapes with the existing tabs first, then enter their net volume;
do not include the current shape again. Waste is applied once to the total.
Existing volume, weight and standard bag outputs reflect the combined order volume including waste. The pour table preserves net quantities before waste. For example, 27 ft³ plus 1 yd³ is 54 ft³; 10% waste produces 59.4 ft³. At 0.6 ft³ per bag, that is 99 whole bags.
Enter the manufacturer's custom bag yield and its volume unit, plus the price per bag. Compare with a ready-mix price per yd³ or m³ and an optional delivery fee. At $5 per bag versus $100/yd³ plus $30 delivery, the example costs $495 bagged or $250 ready-mix. Prices are user inputs, not market quotes. Check minimum loads, extra fees, taxes, labor and mixing equipment separately.