Concrete Calculator
Estimate how much concrete your project needs — in cubic yards or cubic metres, bags, tonnes and cost. Pick a shape, enter your dimensions, and switch between imperial and metric instantly.
Floors, pads, patios, driveways — flat rectangular pours.
How the concrete calculator works
The formula
Concrete volume is simply the space your pour fills. The calculator converts every dimension to metres, multiplies them for the shape you choose, multiplies by quantity, then adds your waste allowance.
- Slab / footing / wall: length × width × thickness.
- Round column or post hole: π × (diameter ÷ 2)² × depth.
- Cubic metres are converted to cubic yards (× 1.308) and cubic feet (× 35.31).
- Weight uses a normal-concrete density of 2,400 kg/m³ (≈ 4,050 lb/yd³).
Worked example
A 20 ft × 20 ft garage slab, 4 inches thick:
- Convert: 20 ft = 6.096 m, 4 in = 0.102 m.
- Volume = 6.096 × 6.096 × 0.102 = 3.78 m³.
- Add 10% waste → 4.16 m³ ≈ 5.44 yd³.
Order about 5.5 cubic yards (4.2 m³) of concrete.
Sizing, thickness & waste
Typical slab thicknesses
- Patios & walkways: 4" (100 mm).
- Driveways & garage floors: 4–6" (100–150 mm).
- Heavy vehicle / industrial slabs: 6–8" (150–200 mm).
Waste allowance
Add 5–10% to your calculated volume to cover spillage, uneven subgrade, and over-excavation. For small or irregular pours, 10% is safer because running short mid-pour creates a cold joint.
What produces this much concrete?
Once you know the volume, the next question is how to produce it. Here is the equipment that matches your pour size:
Small pour — mix on site
Under ~0.5 m³ (≈0.65 yd³) you can mix on site from bags. A portable mixer saves time over hand-mixing once you pass a few bags.
Medium pour — small mixer or ready-mix
From ~0.5–2 m³, a small or self-loading mixer keeps you independent of delivery schedules; otherwise order ready-mix.
Large pour — self-loading mixer or delivery
At 2–10 m³, compare ready-mix delivery against a self-loading mixer or mixer truck if you pour regularly.
On-site batching becomes economical
Above ~10 m³, repeated or remote pours usually cost less with on-site batching than per-load delivery. A mobile or compact plant sets up fast.
Continuous production — dedicated plant
Beyond ~50 m³ per job, a stationary or ready-mix plant delivers the throughput and consistency large projects need.
Frequently asked questions
How do you calculate how much concrete you need?
Measure the pour, multiply length × width × thickness in the same units to get the volume, then convert to cubic yards or cubic metres and add 5–10% for waste. This calculator does all of that for slabs, footings, round columns and walls.
How do you calculate concrete volume?
Volume equals length × width × thickness for rectangular pours, or π × (diameter ÷ 2)² × depth for round columns and post holes. Keep all dimensions in the same unit before multiplying.
How much concrete do I need?
It depends on the size and shape of your pour. Enter your dimensions above and the calculator returns the exact volume in cubic yards and cubic metres, plus bags, weight and cost. As a guide, a 10 ft × 10 ft slab at 4 inches needs about 1.23 cubic yards.
How do you convert concrete volume to cubic yards?
Work out the volume in cubic feet (length × width × thickness, all in feet) and divide by 27, since there are 27 cubic feet in a cubic yard. One cubic yard also equals 0.765 cubic metres.
How do you estimate concrete cost?
Multiply your volume in cubic yards (or cubic metres) by the local concrete price, then add delivery and placement. The concrete cost calculator breaks material, delivery and labour out separately.
How much extra concrete should I order for waste?
Add 5–10% to your calculated volume to cover spillage, uneven subgrade, and over-excavation. For small or irregular pours, 10% is safer because running short mid-pour creates a cold joint.
Are these results accurate enough to order from?
Results are planning estimates. Always confirm volumes, mix designs and structural details with your supplier or engineer before pouring.