Round pads
Concrete Cylinder Calculator
Hot tub pads, silo floors, and fountain rings are circles. Leave the inner diameter at zero unless there is a hole in the middle.
Your region
Feet, inches, cubic yards, and 40–80 lb bags
Concrete Calculator
Example measurements — replace them with yours.
Use 0 for a solid pad. Enter a smaller diameter for a ring.
Common sizes
Most orders add 5–10% for spillage, uneven ground, and the last bit left in the chute.
Cost, truck size, and concrete weight
Leave a price blank to skip that estimate. Use the number your supplier quoted.
This job
Add each pour — slab, piers, steps — and Concrete Calculator totals them.
How to use a concrete cylinder calculator
Area = π × (outer radius² − inner radius²). Multiply by thickness. Inner diameter 0 means a solid pad. Inner ≥ outer is rejected so you do not get a negative pour. Hot tub pads, silo floors, fountain rings, and equipment pads use this shape.
Cylinder and tube searches sometimes want a vertical form instead — use column or sonotube when height is the long dimension and you are filling a tube, not a flat disk.
Worked example with the concrete cylinder calculator
π × 6² × 0.333 ≈ 37.7 ft³ = 1.40 yd³ neat. With 10% ≈ 1.54 → order 1.75 yd³. A ring with 12 ft outer and 8 ft inner at 4 inches is π(36−16)×0.333 ≈ 20.9 ft³ = 0.78 yd³ neat.
Radius vs diameter
Concrete Calculator asks for diameters because tape measurements are usually edge-to-edge. Radius is half of that. Entering a radius into a diameter field doubles the pad and roughly quadruples the volume — check the diagram before you order.
Common mistakes
Entering radius in a diameter field.
- Leaving a phantom inner diameter from a previous ring calculation.
Bags, yards, or a truck?
Around a yard and a half, decide bags vs short load the same way as a small patio.
The formula Concrete Calculator uses
π(R² − r²) × thickness × quantity.
Who this is for
Homeowners pouring spa pads.
Builders placing circular equipment pads.
Round pads vs vertical cylinders
A circular slab calculator is for flat disks and rings. A concrete cylinder calculator search may want a vertical column instead — use column or sonotube when height dominates and you are filling a tube.
Spa pads often sit at 4–6 inches. Confirm the equipment manufacturer’s pad thickness. Rings for fire pits need an inner diameter; leaving a leftover inner diameter from a previous calc will under-order a solid pad.
Worked ring vs solid
Solid 10 ft diameter at 5 inches: π×5²×0.417 ≈ 32.7 ft³ = 1.21 yd³ neat. Same outer diameter with a 6 ft inner opening: π(25−9)×0.417 ≈ 21.0 ft³ = 0.78 yd³. Clear the inner diameter field when you switch back to solid pads.
Related calculators and guides
Open the pages that match the next question on the job — volume is only the first number.
Frequently asked questions
How do I calculate a round pad?
π × radius² × thickness. Radius is half the diameter.
What is inner diameter for?
Cutting a hole for a ring. Use 0 for solid.
Ring footing?
Yes, when the pour is the annular wall or ring itself.
Cylinder column instead?
Use the column or sonotube calculator for vertical tubes.