Pier & Caisson Calculators
Written by Shakeel Alvi · Technically reviewed by Muhammad Qasim, PEC Reg. No. 63430 · Last reviewed: 2026-07-11
Two calculators live here, and the difference between them isn't math — both are a cylinder times a height. It's what holds that cylinder's shape while the concrete is still wet: bare soil, or a manufactured cardboard tube.
Pier / Caisson Concrete Calculator
Cylindrical shafts and drilled piers by length.
Sonotube Concrete Calculator
Volume, cubic yards & bag counts for cylindrical tube forms.
What you're deciding in this category
Start with how the shaft gets its shape. A pier or caisson drilled straight into soil uses the earth itself as the form, so the diameter you enter is the auger's rated cutting diameter, not a guaranteed final dimension — loose, sandy, or rocky ground lets the hole wander wider than the bit, sometimes by an inch or more, and nothing in the volume math catches that until the truck runs short. A Sonotube changes that equation entirely: the tube itself is the form, its printed inside diameter is exact, and the concrete only ever sees the shape the cardboard gives it. The second decision is depth versus load path — a shallow deck footing and a deep foundation caisson use the same formula, but a caisson reaching past a few feet of unsupported height starts answering to slenderness and lateral soil pressure the way a column does, not just to volume. The third is whether the shaft is belled at the bottom, which needs a separate frustum calculation added to the cylinder volume. And below the water table, or in a hole that won't stay dry, placement method matters as much as shape — concrete dropped freely into standing water segregates and loses strength, so a caisson placed wet needs a tremie pipe, which changes crew and equipment planning even though it doesn't change the cubic-yard total the calculator returns.
Which calculator fits which job
The split is entirely about the form, not the job — pick based on whether you're drilling into bare earth or setting a tube.
- Pier / Caisson Concrete Calculator
- Use this for a shaft drilled directly into soil with no manufactured form — deep foundation piers, retaining wall caissons, or any bored shaft where the auger's rated diameter is the input; toggle the belled-bottom option if the base is under-reamed wider than the shaft, and expect actual consumption in loose or rocky ground to run ahead of the stated diameter regardless.
- Sonotube Concrete Calculator
- Use this once a cardboard tube form is set, braced, and cut to length — deck footings, mailbox posts, small pier foundations — where the tube's printed inside diameter is exact and the manufacturer's rated maximum pour height per lift is the real constraint, not the volume math itself.
Standards that govern Pier & Caisson
ACI 336.1 — The construction specification for drilled piers — tolerances on shaft plumbness, minimum concrete slump for placement through a wet hole, and inspection requirements once excavation passes a few feet, which is roughly where soil-formed shafts start needing more than a tape measure to verify, and where a wet hole below the water table triggers the tremie-placement provisions rather than a simple free-drop pour.
ACI 318-19 — Chapter 13 sets the reinforcement and bearing requirements for deep foundations once a pier is doing structural work rather than just carrying a deck — a volume estimate this calculator produces doesn't confirm the shaft is adequately sized or reinforced for the load it will actually carry.
Trusting the auger's rated diameter in loose ground
A power auger is sold with a nominal cutting diameter, and it's tempting to plug that number straight into the calculator and treat the result as final. In firm clay it's close enough. In sand, loose fill, or anything with buried rubble, the bit wanders and the hole comes out wider and less round than rated, sometimes enough to need 10 to 15% more concrete than the nominal diameter predicts. Sonotube pours don't have this problem — the tube holds a fixed shape regardless of what the soil around it is doing — which is exactly why contractors switch to tube forms on ground they don't trust, even when a bare shaft would technically be allowed. The tube costs more per hole and adds a step, but on ground you don't trust it buys back the volume certainty the soil itself won't give you.
Frequently Asked Questions
- What's the difference between a pier and a caisson?
- Mostly terminology and context — a caisson usually implies a larger, sometimes watertight structure built into water or a deep excavation, while a drilled pier is a bored shaft filled with concrete for a foundation. Both use the same cylindrical volume math.
- Why does the diameter I enter not match what actually gets poured?
- An auger's rated diameter assumes clean, firm ground. Loose, sandy, or rocky soil lets the hole wander wider than the bit, so real consumption in that ground commonly runs ahead of the calculator's baseline number.
- Does a Sonotube pour avoid the diameter problem?
- Yes — the tube's printed inside diameter is exact because the tube itself holds the shape, regardless of what the surrounding soil is doing. That certainty is the main reason to choose a tube form over a bare drilled hole.
- How do I calculate a belled pier?
- Add the frustum (cone-shaped) volume of the under-reamed bell to the straight cylindrical shaft volume above it — the pier-caisson calculator's belled-bottom option handles both pieces in one pass.
- Do these calculators account for placing concrete underwater?
- No — a wet hole below the water table needs tremie placement to avoid segregation, which changes crew and equipment needs but not the cubic-yard total either calculator returns.