Concrete Pier Calculator
Pier concrete is a cylinder for the shaft plus, for a belled base, a cone frustum, times the number of piers. Six straight 12 in piers 4 ft deep hold 18.85 ft³ (0.70 yd³); with 15% for over-cut holes, order 0.81 yd³. For tube forms above grade, use the Sonotube Concrete Calculator.
How it's calculated: Volume = [π × (shaft diameter ÷ 2)² × shaft height + bell frustum, if any] × number of piers.
Result appears here
Fill in the fields and press Calculate.
Formula, calculation, assumptions and sources
Shaft = π × (Shaft diameter ÷ 2)² × Shaft height
Bell (if any) = π × Bell height ÷ 3 × (R² + R·r + r²) where R = bell radius, r = shaft radius
Volume = (Shaft + Bell) × number of piers
Run the calculation to see each step with your own numbers.
Six straight piers, 12 in shaft, 4 ft deep, 15% waste.
Shaft = π × 0.5² × 4 = 3.14 ft³ each
Total = 18.85 ft³ = 0.70 yd³ exact
+15%: order 0.81 yd³
- Round shaft of constant diameter.
- The bell is modelled as a cone frustum from the shaft diameter out to the bell diameter over the bell height.
- Reinforcing cage and any permanent casing are not deducted.
- The extra concrete from an over-cut or sloughing hole is covered by the waste allowance, not the geometry.
- Why is the waste higher than other concrete calculators?
- Drilled holes are rarely a clean cylinder — the auger over-cuts and the sides can cave in, especially below the water table. 10–20% extra is normal for piers.
- What is a belled pier?
- A pier with a cone-shaped flared base that spreads the load over more soil, so a smaller shaft can carry more. The bell is cut with a belling tool on the auger. Switch the base to 'belled' and enter the bell diameter and height.
- Is the rebar cage or a permanent casing deducted?
- No — the calculator returns the gross concrete volume for the hole. A cage or casing displaces a little concrete, but the extra from an over-cut hole usually more than makes up for it.
- How much concrete do I need for deck piers?
- Multiply π by the shaft radius squared and by the depth, then by the number of piers. Six 12 in piers 4 ft deep take 18.85 ft³ (0.70 yd³) exact; add 10–20% because augered holes over-cut and slough in.
- How is the volume of a belled pier calculated?
- The bell is treated as a cone frustum: π × bell height ÷ 3 × (R² + R·r + r²), where R is the bell radius and r the shaft radius. That is added to the straight shaft volume above it.
Geometry
Standard geometry — cylinder + cone frustum. Unit conversions per NIST SP 811.
About the Concrete Pier Calculator
The Concrete Pier Calculator gives the concrete for drilled or formed pier foundations — a deck, a pole barn, a boardwalk — with an optional belled base for extra bearing. Enter the shaft diameter and depth, how many piers, and for belled holes the bell diameter and height. Because augered holes over-cut and can slough in, the default waste allowance is higher than the other concrete calculators; raise it further for wet or loose soil. A round tube form above grade is better handled by the Sonotube Concrete Calculator.
What you enter
- Shaft diameter
- Shaft height — Total pier depth for a straight pier; depth above the bell for a belled pier.
- Base
- Bell diameter
- Bell height
- Number of piers
- Waste allowance — Default 10%. Adjust to your own allowance — the exact figure is always shown too.
What you get back
- Concrete volume — shown as the exact figure and, separately, a recommended figure with your waste allowance added.
The formula, a worked example, the assumptions behind it and the sources are shown in full below the calculator.
Related calculators
- Concrete Footing Calculator — Concrete volume for strip and pad footings.
- Concrete Column Calculator — Concrete volume for round or square columns.
- Sonotube Concrete Calculator — Concrete volume for round column forms (Sonotube-style tubes).
- Concrete Calculator for Fence Posts — Concrete volume to set a run of fence posts, allowing for the posts displacing concrete in each hole.
Part of the Concrete calculators.