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Concrete Calculator

Calculate concrete volume and cost for slabs, paths, pads and small footings.

Your estimate

Enter measurements, then calculate.

Planning estimate only. Confirm packaging, coverage, site conditions, and local building requirements before purchasing.

How to measure

Measure the finished length and width of the slab or pad inside the formwork.
Measure depth separately and confirm the design thickness before entering it.
For multiple pads or sections, calculate each section or combine equal-depth rectangles into one total area.
Account for uneven excavation, compacted base variation and formwork bulges before choosing the waste allowance.

Input guide

Depth is entered in centimetres for metric or inches for imperial, while length and width use metres or feet.
Use the planned concrete thickness, not the gravel base thickness.
Waste for concrete is often 5–10% for small projects because under-ordering can be expensive and difficult to fix.
Enter price per cubic metre or cubic yard depending on the selected unit system.

Formula

Volume = length × width × depth × (1 + waste)

Concrete is a volume calculation. The calculator converts depth to the same unit as length and width before multiplying.

Waste is applied to the final volume to allow for uneven ground, spillage, pump or wheelbarrow loss and small measurement errors.

Metric projects return cubic metres. Imperial projects return cubic yards because that is the common ordering unit.

Worked example: Small patio slab

A 4 m by 3 m patio has 12 m² of area.
At 10 cm depth, the raw volume is 1.20 m³.
With 8% waste, the adjusted volume is 1.296 m³.
The calculator rounds this to 1.30 m³ for ordering discussion.

If concrete is 115 USD per m³, the material estimate is about 149.50 USD before delivery, pump charges, reinforcement or finishing labor.

Buying advice

Confirm supplier minimum order size, short-load fees and delivery window before relying on a small-volume estimate.
For structural work, use the engineer’s specified thickness and mix rather than a general calculator assumption.
Have forms, reinforcement and placement tools ready before the truck or mixer arrives.

Common mistakes

Entering depth in centimetres as though it were metres
Forgetting that excavation is rarely perfectly flat
Using outside landscape dimensions instead of inside formwork dimensions
Ignoring minimum order fees for ready-mix delivery
Using a planning calculator for structural design decisions

Verify the formed dimensions before ordering

Concrete volume should come from the inside dimensions of the finished forms and the specified compacted depth. Check several depth points because excavation and subgrade levels are rarely perfectly uniform. Thickened edges, footings, grade beams, steps, and post holes should be calculated as separate shapes.

Do not subtract reinforcement from the volume. For irregular work, keep a written breakdown of each section so the total can be checked independently before a truck or bags are ordered.

Ready-mix and bagged concrete need different checks

For ready-mix, confirm the supplier’s selling unit, minimum load, delivery charge, access limits, and cancellation policy.
For bagged mixes, use the yield printed for the exact bag weight and required mix consistency.
Ask whether the quoted amount includes a pump, short-load fee, waiting time, or disposal of returned concrete.
Plan labor, tools, water, placement route, and finishing before mixing or dispatch.
Keep the order calculation and supplier confirmation in the same unit.

Structural design is outside this estimate

The calculator estimates geometric volume and user-entered cost only. It does not choose slab thickness, concrete strength, reinforcement, joints, drainage slope, foundations, curing method, or weather limits.

Use dimensions and specifications from the responsible designer or local requirements for structural, load-bearing, elevated, vehicle, pool, retaining, or permitted work. An apparently small change in depth can materially change both safety and quantity.

Frequently asked questions

How much extra concrete should I order?

For small slabs, 5–10% is common. Complex forms, uneven excavation and hand mixing may need more.

Does this calculate bags of concrete?

This version estimates volume and cost. Bag count depends on the yield printed on the specific bag.

Can I use this for footings?

You can estimate simple rectangular footing volume, but structural sizing must come from local code or an engineer.

Why is depth a separate small-length field?

Slab depth is usually measured in centimetres or inches, while length and width are measured in metres or feet.

Does the result include reinforcement?

No. Rebar, mesh, vapor barrier, base material and finishing labor are separate items.