Concrete Calculator

Estimate concrete volume for a rectangular pour from length, width and thickness, with cubic yards, cubic metres, bag estimates, ready-mix cost, visible overage and a printable pour-planning record.

Concrete needed12 ft × 10 ft × 4 in × 1 pour(s) = 40 ft³ (1.481 yd³) base · plus 10% = 44 ft³ · 1.246 m³ · about 74 bag(s) at 0.6 ft³/bag

Pour lengthftPour widthftThicknessinMatching poursOverage / waste allowance%Bag yieldft³/bag

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Your numbers, formula and explanation together

Concrete Calculator: 1.63 yd³. 12 ft × 10 ft × 4 in × 1 pour(s) = 40 ft³ (1.481 yd³) base · plus 10% = 44 ft³ · 1.246 m³ · about 74 bag(s) at 0.6 ft³/bag

Formula applied

The exact method behind this answer

CalculationTime keeps the method visible so the number can be checked instead of blindly trusted.

Thickness feet = thickness inches ÷ 12. Base cubic feet = length × width × thickness feet × matching pours. Base cubic yards = base cubic feet ÷ 27. Order cubic yards = base cubic yards × (1 + overage percent ÷ 100). Cubic metres = order cubic yards × 0.764554857984. Bags needed = ceiling(order cubic feet ÷ bag yield). Optional ready-mix cost = order cubic yards × price per cubic yard.

Apply the formulaThickness feet = thickness inches ÷ 12. Base cubic feet = length × width × thickness feet × matching pours. Base cubic yards = base cubic feet ÷ 27. Order cubic yards = base cubic yards × (1 + overage percent ÷ 100). Cubic metres = order cubic yards × 0.764554857984. Bags needed = ceiling(order cubic feet ÷ bag yield). Optional ready-mix cost = order cubic yards × price per cubic yard.1.63 yd³12 ft × 10 ft × 4 in × 1 pour(s) = 40 ft³ (1.481 yd³) base · plus 10% = 44 ft³ · 1.246 m³ · about 74 bag(s) at 0.6 ft³/bag

Your live breakdown

Current inputs in the calculation

These values come from the controls above and update when the calculator changes.

Pour length: 12 ft
Pour width: 10 ft
Thickness: 4 in
Matching pours: 1
Overage / waste allowance: 10 %
Bag yield: 0.6 ft³/bag
Optional ready-mix price: 0 $/yd³

Resulting answer

1.63 yd³

12 ft × 10 ft × 4 in × 1 pour(s) = 40 ft³ (1.481 yd³) base · plus 10% = 44 ft³ · 1.246 m³ · about 74 bag(s) at 0.6 ft³/bag

Answer: 1.63 yd³
Live support: 12 ft × 10 ft × 4 in × 1 pour(s) = 40 ft³ (1.481 yd³) base · plus 10% = 44 ft³ · 1.246 m³ · about 74 bag(s) at 0.6 ft³/bag

Assumptions used

What this answer assumes

Best for homeowner slab planning, small pads, paths, shed bases, quote notes, supplier calls and classroom trade-math examples where dimensions, thickness and overage need a printable paper trail.

The calculator treats each pour as a rectangular prism. Split L-shaped or irregular pours into separate rectangles before adding them together.
Thickness is converted from inches to feet before volume is calculated.
Cubic yards use the exact relationship 1 cubic yard = 27 cubic feet.
Bag count is rounded up because dry concrete mix is normally bought in whole bags.
This is a quantity estimate, not a structural design, code-compliance, reinforcement, subgrade, curing, slump, delivery or safety assessment.

Master’s Tip

How to use the result well

Master’s Tip: print the base volume and order volume separately. A quote note that only says “1.63 yd³” is hard to audit unless the dimensions, thickness, overage and bag-yield assumptions stay attached.

Printable record

What belongs in the saved calculation

Save the inputs, result, formula, assumptions, page URL and date together so the calculation can be reviewed later.

Pour length: 12 ft
Pour width: 10 ft
Thickness: 4 in
Matching pours: 1

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Formula

Thickness feet = thickness inches ÷ 12. Base cubic feet = length × width × thickness feet × matching pours. Base cubic yards = base cubic feet ÷ 27. Order cubic yards = base cubic yards × (1 + overage percent ÷ 100). Cubic metres = order cubic yards × 0.764554857984. Bags needed = ceiling(order cubic feet ÷ bag yield). Optional ready-mix cost = order cubic yards × price per cubic yard.

Worked example

For a 12 ft × 10 ft slab at 4 in thick, thickness = 4 ÷ 12 = 0.3333 ft. Base volume = 12 × 10 × 0.3333 = 40 ft³, or 1.4815 yd³. With 10% overage, order volume is about 1.63 yd³.

Professional note

Regional and unit assumptions

Standard or basis: rectangular-prism volume takeoff using feet, inches and cubic yards, with 1 yd³ = 27 ft³ and 1 yd³ = 0.764554857984 m³. Concrete strength, reinforcement, joints, base preparation, curing and local code requirements must be checked separately.

Assumptions and limitations

The calculator treats each pour as a rectangular prism. Split L-shaped or irregular pours into separate rectangles before adding them together.
Thickness is converted from inches to feet before volume is calculated.
Cubic yards use the exact relationship 1 cubic yard = 27 cubic feet.
Bag count is rounded up because dry concrete mix is normally bought in whole bags.
This is a quantity estimate, not a structural design, code-compliance, reinforcement, subgrade, curing, slump, delivery or safety assessment.

Methodology & Accuracy

How this calculator is checked

CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.

Formula used

Standard or basis

Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.

Master's Tip

Questions

How do I calculate how much concrete I need?

Multiply length by width by thickness in feet to get cubic feet, then divide by 27 to get cubic yards. Add a visible overage allowance before ordering.

How many cubic feet are in a cubic yard of concrete?

There are exactly 27 cubic feet in one cubic yard. A cubic yard is 3 ft × 3 ft × 3 ft.

What overage should I use for concrete?

A 5% to 10% allowance is often used for small planning estimates, but uneven subgrade, forms, pump lines and site conditions can change the order. Keep the allowance visible rather than hiding it in the dimensions.

Can I use bag yield for ready-mix concrete?

Bag yield is for dry bagged concrete products. Ready-mix is normally ordered by cubic yard or cubic metre, so use the cubic-yard result and supplier guidance for truck delivery.

What should I print for a concrete pour note?

Print the length, width, thickness, matching sections, base cubic feet, order cubic yards, overage, bag yield, formula, page URL, date and notes for reinforcement, forms, subgrade and supplier discussion.

Calculation note

Concrete estimating is a volume problem, but the useful record is a pour note: dimensions, thickness, base cubic feet, order cubic yards, allowance, bag yield and supplier assumptions all belong together.

Concrete quantity starts with volume

For a simple slab or pad, the arithmetic is length × width × thickness. The common mistake is leaving thickness in inches instead of converting it to feet before multiplying.

Cubic yards are the ready-mix language

In the United States and many trade contexts, ready-mix concrete is quoted in cubic yards. Showing cubic feet, cubic yards and cubic metres makes the record easier to compare across suppliers and classroom examples.

Overage should stay visible

A separate overage line is more honest than quietly inflating dimensions. It lets another person see what was measured and what was added for site uncertainty.

Sources and further readingNIST Handbook 44 Appendix C — General Tables of Units of Measurement NIST SP 811 — Guide for the Use of the International System of Units Portland Cement Association — Concrete basics