Concrete Volume Calculator
Estimate how much ready-mix concrete to order for a rectangular slab, footing, or pad. Enter length, width, and depth in metres, plus a waste percentage (preset to 5%), and the page returns the order volume in cubic metres with the waste allowance already applied.
Your result will appear here.
Concrete Volume Calculator online
Calculate the concrete volume of a rectangular pour with the waste allowance built in — length × width × depth, grossed up by the percentage you choose — for slabs, patios, paths and pads.
How it works
The calculation is Volume = L × W × D × (1 + Waste ÷ 100). All three dimensions must be in metres, so convert centimetres first: a 150 mm slab is 0.15 m. The waste field covers spillage, uneven subgrade, and formwork leakage. Leaving it at the default 5% suits flat, well-prepared ground; use 7–10% for rough subgrade, intricate formwork, or long pump lines.
Worked example
A patio slab 6 m long, 4 m wide, and 0.15 m thick with 5% waste: net volume = 6 × 4 × 0.15 = 3.6 m³; order volume = 3.6 × 1.05 = 3.78 m³, so order 3.8 m³ (or round to 4 m³). In US ordering units that is 3.78 × 1.308 ≈ 4.94 yd³, so a 5 yd³ load covers it; in cubic feet it is 3.78 × 35.3147 ≈ 133.5 ft³.
Units
The result is always in cubic metres. Useful equivalents: 1 m³ = 35.3147 ft³ = 1.308 yd³, and 1 yd³ = 0.7646 m³. Thickness conversions worth memorising: 4 in = 10.16 cm, 5 in = 12.7 cm, 6 in = 15.24 cm. US batch plants sell by the cubic yard and often add a short-load fee below 3–4 yd³; elsewhere concrete is sold by the cubic metre.
Practical tips
- Check depth at several points with a tape before ordering; a subgrade that averages 17 cm instead of 15 cm adds over 13% to the volume.
- Enter all dimensions in metres in one pass. Typing 15 for depth when the label expects metres turns a 3.6 m³ slab into a 360 m³ order.
- Round up to the supplier’s minimum increment. A second truck for half a metre costs far more than ordering slightly heavy.
- This page estimates quantity only. Confirm the strength grade, slump, aggregate size, and reinforcement with your drawings and supplier, and have any structural choices signed off by a qualified engineer.
Edge cases and limitations
- Average a sloped soffit. On sloping or cambered pours, average the shallowest and deepest readings for D; on a visibly dished subgrade, average a grid instead. Depth error dominates every other input — a 10 mm error on a 150 mm slab is 7% of the order.
- Multiple elements, one order. Run each element separately and add the order volumes, rather than averaging dimensions across different shapes. Keep the waste percentage consistent across the runs so the total margin is predictable.
- Thickenings and edge beams. A slab with a thickened edge is two volumes: the flat slab at its nominal depth, plus the edge beam as its own rectangle below it. Forgetting the thickening is the classic 10–15% under-order on raft slabs.
- Round to how concrete is sold. Suppliers batch in 0.5 m³ (or 0.5 yd³) steps and surcharge part loads. An order volume of 3.78 m³ becomes a 4 m³ order — the rounding is part of the estimate, not an afterthought.
Privacy and browser processing
The calculation runs entirely in your browser — the dimensions you enter are never uploaded.
Frequently asked questions
How much waste should I add for a concrete slab?
Keep the preset 5% for flat, compacted subgrade with simple formwork. Raise it to 8–10% for hand-dug ground, stepped edges, or pumped pours. On the 6 × 4 × 0.15 m example, 5% gives 3.78 m³ while 10% gives 3.6 × 1.10 = 3.96 m³.
Why does the result change when I type depth as 15 instead of 0.15?
The depth field expects metres, so typing 15 means a 15-metre-deep block: 6 × 4 × 15 = 360 m³ instead of 3.6 m³. Always convert first — 100 mm = 0.10 m, 125 mm = 0.125 m, 150 mm = 0.15 m — then enter the decimal value.
How do I convert the result to cubic yards?
Multiply cubic metres by 1.308. The worked example gives 3.78 × 1.308 ≈ 4.94 yd³, so you would order 5 yd³. Going the other way, multiply cubic yards by 0.7646: a 5 yd³ ticket equals about 3.82 m³.
Does this replace the Concrete Calculator page?
Both pages use the same L × W × D plus waste formula, so either gives the same number for a rectangular pour. Use this page when you think in terms of order volume in m³; use the bag-count and mix-ratio pages when you need bag quantities or cement, sand, and gravel splits.