How much concrete for a round form?
Round concrete forms are calculated as cylinders. Use inside diameter, height or depth, and count, then convert the total volume to cubic yards or bags.
Diameter has a big effect
Cylinder volume uses radius squared, so a small increase in diameter can noticeably increase concrete quantity. Measure the inside diameter of the form or hole.
Tubes, piers, columns, and holes
Tube forms, piers, columns, and round holes use similar volume math, but their structural requirements can be very different. This page estimates material quantity only.
Common concrete slab sizes
Cubic yards below are before waste. Add your project waste percentage before ordering.
| Slab size | 4 in thick | 5 in thick | 6 in thick |
|---|---|---|---|
| 10 ft x 10 ft | 1.23 cu yd | 1.54 cu yd | 1.85 cu yd |
| 10 ft x 12 ft | 1.48 cu yd | 1.85 cu yd | 2.22 cu yd |
| 12 ft x 12 ft | 1.78 cu yd | 2.22 cu yd | 2.67 cu yd |
| 20 ft x 20 ft | 4.94 cu yd | 6.17 cu yd | 7.41 cu yd |
| 24 ft x 24 ft | 7.11 cu yd | 8.89 cu yd | 10.67 cu yd |
| 30 ft x 40 ft | 14.81 cu yd | 18.52 cu yd | 22.22 cu yd |
Before you calculate
- Enter the inside form diameter, not the outside packaging size.
- Measure height or depth consistently for each tube.
- Use the count input when several identical forms are being poured.
Common mistakes
- Estimating round forms as rectangles.
- Mixing inches and feet for diameter and height.
- Forgetting that over-excavation or an uneven bottom can increase concrete demand.
Formula
cubic yards = (length * width * (thickness / 12) / 27) * (1 + wastePercent / 100)
Assumptions
- Concrete quantity is a planning estimate, not structural design.
- Thickness, subgrade, forms, reinforcement, slopes, and local requirements should be checked separately.
- Round ready-mix, bagged materials, form parts, and coatings up before ordering.
Example
Estimated concrete needed (cubic yards): 0.61 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 Reading shed Pier Concrete Pad Calculator result to plan materials.
Before you buy materials
- Round the result up to match ready-mix ordering or bag yield increments.
- Confirm form size, bracing, and placement before using the estimate for ordering.
FAQ
What is the example reading shed pier 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 0.61 cubic yards.
How do I calculate concrete for a sonotube or tube form?
Calculate the cylinder volume from diameter and height, multiply by count, add waste, then convert to cubic yards or bags.
Do I use inside or outside diameter?
Use inside diameter because that is the space the concrete fills.
How do I calculate multiple piers?
Calculate one pier, then multiply by the number of identical piers. Calculate different pier sizes separately.
Does this design a structural pier or column?
No. It estimates concrete quantity only. Structural sizing and reinforcement require qualified guidance.
Related calculators
This calculator is for planning estimates only. Verify final quantities with product labels, project conditions, and a qualified professional when accuracy matters.