Slabs, shed pads and footings — order by the yard
Concrete Calculator
Concrete volume in cubic yards = length × width × thickness (all in feet) ÷ 27. A 10 ft × 10 ft slab 4 inches thick needs about 1.4 cubic yards with 10% extra. Enter your dimensions to see yards, weight and cost.
Cubic yards to order
1.36 yd³
- Exact volume, before extra
- 1.235 yd³
- Estimated weightTypical density; moisture changes it.
- 2.72 US tons
- Cubic feet
- 36.67 ft³
- Cubic meters
- 1.038 m³
- Estimated cost
Worked examples
Patio slab
A 12 ft × 12 ft slab, 4 inches thick, 10% extra.
1.96 yd³ · ≈ 3.91 US tons
Shed pad
An 8 ft × 10 ft pad, 6 inches thick, 5% extra.
1.56 yd³ · ≈ 3.11 US tons
Circular fire-pit pad
A 6 ft diameter circle, 4 inches thick, 10% extra.
0.38 yd³ · ≈ 0.77 US tons
Good for
- Patio and shed slabs before you call a ready-mix plant
- Estimating bag counts for tiny pads where a truck minimum does not make sense
- Circular pads (fire pits, basketball hoops) without a separate spreadsheet
- Ballparking cost once you know the plant’s price per yard
Common mistakes
- Mixing inches and feet in the same multiply step
- Ordering exact volume with no extra on uneven subgrade
- Thinking this volume includes rebar, mesh or base rock
- Using a patio thickness for a driveway that needs a thicker section
How to calculate concrete volume
- Convert thickness to feet. Four inches ÷ 12 = 0.333 ft.
- Multiply length × width × thickness in feet to get cubic feet.
- Divide by 27 to get cubic yards.
- Add waste: many pours order about 5–10% extra.
- Ready-mix is usually ordered by the cubic yard; bagged mix is sold by bag yield (check the bag).
This calculator estimates volume only. Reinforcement, forms, subbase and mix design are separate decisions.
Concrete coverage by thickness
Cubic yards to cover 100 square feet. Multiply by your area ÷ 100.
| Depth | Cubic yards per 100 sq ft |
|---|---|
| 3.5 in | 1.08 |
| 4 in | 1.23 |
| 5 in | 1.54 |
| 6 in | 1.85 |
Approximate weight per cubic yard
Normal-weight concrete is often near 2 short tons per cubic yard; lightweight mixes weigh less.
| Material | US tons per cubic yard (typical range) | Value used here |
|---|---|---|
| Concrete | ≈ 2.0 | 2 |
Frequently asked questions
How thick should a concrete slab be?
Many residential patio and shed pads use about 4 inches. Driveways and areas with heavier loads often need 5–6 inches or more plus a proper base. Follow local code or an engineer’s spec for structural work.
How many 80 lb bags make a cubic yard?
An 80 lb bag of concrete mix commonly yields about 0.60 cubic feet. One cubic yard is 27 cubic feet, so you need roughly 45 bags—before waste. Always check the yield printed on the bag.
Why order extra concrete?
Forms may be slightly oversized, the subgrade may be uneven, and shorting a pour is expensive. A modest extra percentage is normal for small residential jobs.
Does this include rebar or wire mesh?
No. Volume is only the concrete. Reinforcement, vapor barriers and base rock are separate line items.
Sources and updates
Last reviewed .
- NIST – Unit conversion factors – Length definitions used for unit conversion.
- Concrete density – Typical normal-weight range near 2 US tons per cubic yard. Confirm mix data with your supplier.
Estimates for planning only. Structural pours need local code compliance and often a professional design.