How much concrete for a slab?
Concrete slabs are ordered by volume, not just square footage. Multiply slab length by width, convert thickness from inches to feet, then divide by 27 to get cubic yards. Add a practical waste buffer before ordering.
Common slab sizes
A 10 x 10 ft slab at 4 inches thick is about 1.23 cubic yards before waste. A 12 x 12 ft slab at 4 inches thick is about 1.78 cubic yards. A 20 x 20 ft slab at 4 inches thick is about 4.94 cubic yards.
Slab thickness and waste
Thickness changes concrete volume quickly. Moving from 4 inches to 6 inches increases the volume by 50%. Uneven base, forms, and ordering variance are common reasons to add waste.
Linear concrete run examples
Examples are before waste. Measure changed-width sections, returns, corners, and transitions separately.
| Project example | Run x width x depth | Cubic yards |
|---|---|---|
| Narrow curb or mow strip | 50 ft x 0.5 ft x 6 in | 0.46 cu yd |
| Standard curb run | 100 ft x 0.5 ft x 6 in | 0.93 cu yd |
| Curb and gutter pan | 100 ft x 1.5 ft x 6 in | 2.78 cu yd |
| Trench or channel fill | 40 ft x 1 ft x 12 in | 1.48 cu yd |
Before you calculate
- Measure the total run length in feet and calculate separate runs when width or depth changes.
- Enter the formed width and thickness instead of using the visible top surface only.
- Keep waste visible for over-excavation, uneven subgrade, short forms, corners, and transitions.
Common mistakes
- Treating a curb or trench like a broad slab and forgetting depth changes along the run.
- Combining straight runs, returns, radiused corners, and driveway transitions without measuring them separately.
- Using a quantity calculator as drainage, reinforcement, slope, or code design.
Formula
cubic yards = (length * width * (thickness / 12) / 27) * (1 + wastePercent / 100)
Assumptions
- Concrete quantity is a planning estimate, not structural design.
- Thickness, forms, subgrade, reinforcement, drainage, slopes, and local requirements should be checked separately.
- Round ready-mix, bags, forms, sealers, and accessories up before ordering.
Example
Estimated concrete needed (cubic yards): 1.2 cubic yards
How to use this calculator
- Enter length in ft.
- Enter width in ft.
- Enter thickness in in.
- Enter waste in %.
- Review the live estimate and compare it with the example result.
- Check the formula, assumptions, product labels, and site conditions before using the Stormwater Side Yard Trench Drain Cover Stand Concrete Pad Calculator result to plan materials.
Before you buy materials
- Use the result as a ready-mix or bagged-concrete planning number, then round by supplier rules.
- Plan forms, stakes, base, reinforcement, drainage slope, joints, finishing, and cleanup as separate lines.
FAQ
What is the example stormwater side yard trench drain cover stand concrete pad cubic-yard result?
Use length, width, thickness or depth, and waste, then calculate the planning result. In the default example, the result is 1.2 cubic yards.
How do I calculate concrete for a slab?
Use cubic yards = (length x width x (thickness / 12)) / 27, then add waste if needed. Measure length and width in feet and thickness in inches.
How much concrete is needed for a 10 x 10 slab?
At 4 inches thick, a 10 x 10 ft slab needs about 1.23 cubic yards before waste. With 10% waste, plan around 1.36 cubic yards.
Does slab thickness matter?
Yes. A 4 inch slab and a 6 inch slab with the same footprint require different volumes. This calculator estimates quantity, not the required structural thickness.
Should I order ready-mix or bags for a slab?
Small slabs may be possible with bags, but larger slabs often make more sense as ready-mix. Compare cubic yards, bag yield, labor, delivery, and supplier minimums.
Related calculators
This calculator is for planning estimates only. Verify final quantities with product labels, project conditions, and a qualified professional when accuracy matters.