SettingsSettings for this calculationUS
The diameter of the straight drilled shaft.
Measure the drilled hole diameter, not including any casing wall thickness.
The straight shaft length, not including any bell at the base.
Measure from the top of the pier to the top of the bell (or to the bottom if there's no bell).
Whether the pier has an enlarged base (bell) for extra bearing capacity.
Belled piers spread load over a larger bearing area at the base without needing a larger shaft diameter throughout.
Total concrete volume
3.03 yd³
Assumes an idealized frustum-shaped bell — actual drilled bell geometry can vary with the drilling equipment and soil conditions; verify final volume against the driller's as-built log.
- Straight shaft volume
- 3.03 yd³
- Bell volume
- 0 yd³
They open the calculator with your figures already in it
Drilled Pier Concrete Volume Calculator (Straight Shaft / Belled): 3.03 yd³ — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Straight shaft volume = pi x radius² x length; an under-ream (bell) is a frustum of a cone, volume = (pi x height / 3) x (R² + Rr + r²), where R is the bell radius and r is the shaft radius
Inputs used
- Shaft Diameter
- 2 ft
- Shaft Length (Above Bell)
- 26 ft
- Pier Type
- Straight shaft (no bell)
- Bell Diameter
- 5 ft
- Bell Height
- 3.5 ft
Intermediate steps
- Straight shaft volume
- 3.03 yd³
- Bell volume
- 0 yd³
Confidence note: Assumes an idealized frustum-shaped bell — actual drilled bell geometry can vary with the drilling equipment and soil conditions; verify final volume against the driller's as-built log.
What this calculation does not cover
- This is the theoretical volume of one drilled hole, with no allowance for over-break. A drilled shaft almost always takes more concrete than its design diameter implies, because the auger and any sloughing leave a hole wider than the drawing, and no waste or over-break factor is applied here. Add one before ordering, and multiply by the number of piers.
- The bell is treated as a plain cone frustum running straight from the shaft to the bell diameter. A real under-ream has a short vertical toe at the base and follows the shape of the reaming tool, so entering a bell height measured off a drawing understates the concrete the toe holds.
- Nothing here is a foundation design. Shaft diameter, depth, bell size, bearing pressure and skin friction all come from a geotechnical report and the structural drawings; this takes those dimensions as given and returns a volume, and says nothing about whether they are adequate.
- Whether the ground will hold an open bell is not assessed. Under-reams need cohesive soil that stands unsupported while the bell is cut; in granular, running or water-bearing ground a bell cannot be formed safely and the pier is built straight-shafted or cased instead.
- Excludes concrete placed above the design cut-off, which drilled shafts are normally over-poured to reach sound material, and the extra taken when temporary casing is withdrawn and concrete slumps out into the annulus.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Straight shaft volume = pi x radius² x length; an under-ream (bell) is a frustum of a cone, volume = (pi x height / 3) x (R² + Rr + r²), where R is the bell radius and r is the shaft radius
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