Waste slider first
5% for a flat, simple slab; 10% is the default for typical yards; 15–20% for stairs, columns, or awkward forms. Waste applies after all shapes are summed if you run several entries.
Concrete & cubic yards
Concrete Calculator
Cubic yards and bag counts for slabs, columns, stairs, and curbs with adjustable waste.
By Jeff Beem
Updated
Project dimensions
10%
Add 5–10% for spillage and uneven subgrade
Results
0.90
Cubic yards
Cubic feet24.28
Cubic meters0.69
Bagged concrete
40 lb bags82
60 lb bags53
80 lb bags41
Estimated weight1.80 tons (3,597 lbs)
Based on 4,000 lbs per cubic yard
Example: 5 m × 2.5 m slab, 5 cm thick
Default slab: 5 m long, 2.5 m wide, 5 cm thick, 10% waste → about 0.90 yd³ to order (~41 eighty-pound bags). That is roughly 0.63 m³ net before waste. Change shape for columns, stairs, curb/gutter, or hollow cylinders.
What the numbers mean
Yards vs bags
Ready-mix is quoted in cubic yards (or meters). Bags are counted with yields of 0.011 / 0.017 / 0.022 yd³ for 40 / 60 / 80 lb mixes. Past ~1 yd³, compare truck price before buying pallets.
Weight line
About 4,000 lb per cubic yard helps sanity-check truck capacity and whether forms or soil need extra prep before the pour.
Mix shapes on one job
Run slab, footing, column, stair, or curb entries separately, add mentally or in sequence, then set one waste percent on the total you will order.
Concrete calculator: yards, bags, and waste
5 m × 2.5 m × 5 cm slab, 10% waste: ~0.90 yd³ (~41 × 80 lb bags). Slabs, columns, stairs, curbs; imperial or metric inputs.
What this calculator does
Computes concrete volume for slabs, round columns, hollow cylinders, stairs, and curb/gutter sections, then adds your waste percent, converts to cubic yards or meters, estimates bag counts, and shows wet weight. It does not pick mix design, rebar, or cure times.
- Default slab:5 m × 2.5 m × 5 cm + 10% waste ≈ 0.90 yd³; ~41 bags at 80 lb; ~3,600 lb wet weight.
- US patio example:10 ft × 10 ft × 4 in ≈ 1.23 yd³ before waste (add 10% → ~1.35 yd³).
- Limits:Planning math only; verify with supplier specs, pump reach, and local codes.
Volume by shape
Slab or footing
Volume = length × width × thickness (same units, converted internally).
- Formula:V = L × W × T
- Thickness hints:Sidewalks/patios often 4 in; driveways 4–6 in; many footings 6–8 in.
Round column
Solid cylinder: π × r² × height. Hollow cylinder uses outer minus inner radius.
- Example:12 in diameter, 8 ft tall ≈ 0.23 yd³ per column before waste.
Stairs
Each step is modeled as a rectangular block with cumulative rise. Enter run, rise, width, step count, optional platform depth.
- Tip:Use 10–15% waste; form losses run higher than flat slabs.
Curb and gutter
Curb prism + gutter prism + optional flag thickness along the run length.
- Example:50 ft run with 6 in curb and 12 in × 4 in gutter ≈ 1.08 yd³ before waste.
Waste and ordering
Subgrade dips, chute spill, and overfilling forms are why contractors rarely order net volume. Simple slabs: 5%. Typical backyard work: 10% default. Stairs and columns: consider 15–20%. Ready-mix plants often want ≥1 yd³; bag counts round up per bag size yield.
Bag yields
Common US yields: 40 lb ≈ 0.011 yd³, 60 lb ≈ 0.017 yd³, 80 lb ≈ 0.022 yd³. Divide total yards (with waste) by yield and round up. At 0.90 yd³ with waste, eighty-pound bags land near 41; a full yard with waste is about 50 bags.
FAQ
How much concrete do I really need?
Order a little over the math. Uneven subgrade, spill at the chute, and form overfill eat volume. Most residential pours use 5–10% extra; this tool defaults to 10%.
How thick should a driveway slab be?
Many residential driveways run 4–6 inches thick; heavier loads may need 6–8 inches. Enter length, width, and thickness here; waste is applied on top.
How many 80lb bags are in a cubic yard?
About 45 eighty-pound bags per cubic yard at roughly 0.022 yd³ yield per bag. The results panel rounds up bag counts for 40, 60, and 80 lb once volume is set.
What is the difference between bagged and ready-mix concrete?
Bagged suits patches and small pours with no truck minimum. Ready-mix is delivered by the yard; past about one cubic yard it is usually cheaper and faster than hand-mixing bags.
How do I calculate concrete for stairs?
This tool models each step as a block (run × rise × width, cumulative rise). Pick Stairs, enter run, rise, width, and step count. Bump waste toward 15% for tight formwork.
What is a waste factor and why do I need it?
It is spare concrete for spillage, low spots in the subgrade, and overfilled forms. Need 10 yd³ net? At 10% waste, order about 11 yd³. Running out mid-pour forces cold joints.
How much does concrete weigh?
Wet concrete is about 4,000 lb per cubic yard (~2,400 kg/m³). The panel multiplies your yardage for a rough load estimate on trucks and base prep.
What is the minimum order for ready-mix concrete?
Many plants enforce about a one cubic yard minimum. Under that, bagged mix is usually the practical route; the panel shows both yardage and bag counts.
DIY Estimation Note
Estimates Only: These calculators provide theoretical estimates based on standard dimensions. Material density, waste factors, and specific project conditions vary significantly.
Verify Locally: Always verify measurements and material requirements with a professional contractor or local building codes before purchasing supplies or starting work.
Project Accuracy: CalcRegistry is not responsible for material shortages, overages, or structural issues resulting from the use of these general estimates.
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