Concrete Calculator
Estimate how much concrete you need for a slab, footing, or pad. Enter the length, width, and depth of a rectangular placement and get the volume instantly — then add a waste allowance so you do not come up short on pour day.
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Concrete Calculator online
Estimate concrete volume from length, width and depth for slabs, pads and other rectangular placements — with the unit conversions, waste allowances and ordering judgement that a raw multiplication leaves out.
How it works
Concrete volume is length × width × depth: Volume = L × W × D. All three dimensions must use the same unit. If the page is set to metres, enter metres; a 15 cm slab is 0.15 m, not 15. Mixing units (metres for length, centimetres for depth) is the most common mistake and inflates the result 100-fold.
Worked example
A driveway slab 6 m long, 4 m wide, 0.15 m thick: net volume = 6 × 4 × 0.15 = 3.6 m³. Add 5–10% waste for spillage, uneven subgrade, and formwork gaps → 3.8–4.0 m³ to order. In US units: 3.6 m³ × 1.308 ≈ 4.7 yd³ — order 5 yd³ from the batch plant. For small jobs, a standard 80 lb (36.3 kg) bag yields about 0.017 m³, so 3.6 m³ would need roughly 212 bags — a ready-mix truck is cheaper at that scale.
Units
- 1 m³ = 35.31 ft³ = 1.308 yd³
- 1 yd³ = 0.7646 m³
- Thickness: 4 in = 10.16 cm; 6 in = 15.24 cm
Batch plants in the US sell by the cubic yard and charge a short-load fee below their minimum (often 3–4 yd³); plants elsewhere sell by the cubic metre.
Practical tips
- Measure twice. Re-measure depth at several points — subgrade is rarely perfectly level, and depth errors dominate volume errors.
- Always round up. Ordering 5% extra is far cheaper than a second delivery.
- Convert before you type. Enter values in one unit system; do not convert mid-form.
- This is a quantity estimate, not a mix design. It tells you how much concrete, not the strength grade, slump, or reinforcement your project needs.
Edge cases and limitations
- Round shapes. The formula here is for rectangles. For a round footing or column base, use the cylinder volume π × r² × depth: a 0.4 m diameter hole 1 m deep is 3.1416 × 0.2² × 1 ≈ 0.126 m³ per footing. Add up all footings, then apply waste.
- Sloped or dug-out ground. A single depth reading lies on uneven subgrade. Measure the depth on a grid, average the readings, and use that as D — hollows you cannot see are where "missing" concrete goes.
- Pumping eats volume. A pump line holds roughly 0.2–0.5 m³ that never reaches the forms, and priming wastes more. On pumped jobs, add that on top of the waste percentage rather than inside it.
- Stairs and triangles. Approximate each step as a triangle (½ × going × rise × width) and sum the steps; a straight flight usually lands near half the volume of the solid block it sits in.
- What the number is not. Volume says nothing about strength grade, slump, air entrainment or reinforcement — those come from your specification and supplier, not from a quantity estimate.
Privacy and browser processing
The calculation runs entirely in your browser — the dimensions you enter are never uploaded.
Frequently asked questions
How much extra concrete should I order?
Add 5% for flat, well-prepared subgrade and up to 10% for irregular ground, complex formwork, or long pump lines. Round the total up to the nearest half cubic metre (or cubic yard).
How do I convert cubic metres to cubic yards?
Multiply m³ by 1.308. Ordering in the US is usually by cubic yard: 3.6 m³ ≈ 4.7 yd³.
Does the calculator account for reinforcement?
No. Rebar displaces a small amount of concrete (usually under 2% for typical slabs); the waste allowance more than covers it.
Is this suitable for final ordering?
Treat it as a planning estimate. Confirm dimensions against project drawings, check the mix design and specifications with your supplier, and have structural decisions reviewed by a qualified professional.