Field calculator
Sonotube pier concrete calculator (round column)
Round piers and columns formed with cardboard tubes need their concrete figured as a cylinder, and the volume is pi times the radius squared times the height. Enter the tube diameter in inches, the height or depth in feet, and the number of piers, and the tool returns the total in cubic feet and cubic yards plus an approximate bag count, using about 0.6 cubic foot per 80-pound bag and 0.45 per 60-pound bag. This is the straight cylinder volume, so add concrete for over-excavation, for a belled or flared footing at the base, and for waste, and round up. The economics shift with quantity: bagged concrete is fine for one or two small piers, but past a few it is usually cheaper and far faster to order ready-mixed by the yard. The pier diameter and depth are not a rule of thumb either, they are set by the load the pier carries, the bearing capacity of the soil, and the local frost depth, since a footing above the frost line heaves. Confirm the pier size, the depth, and any reinforcement with the structural engineer and the geotechnical report.
Result
Round pier (sonotube) concrete: volume = pi × radius squared × height, for a cylindrical column or pier form. Enter the tube diameter in inches, the height or depth in feet, and the number of piers, and the tool returns the total cubic feet, cubic yards, and an approximate bag count (about 0.6 cubic foot per 80-pound bag, 0.45 per 60-pound bag). This is the straight cylinder volume, so add concrete for over-excavation, for a belled or flared footing at the bottom, and for waste, and round up. The economics flip with quantity: bagged concrete is fine for one or two small piers, but past a few it is usually cheaper and faster to order ready-mixed. The pier diameter and depth are not a guess either, they are set by the load, the bearing soil, and the local frost depth, so confirm the size, the depth, and any reinforcement with the structural engineer and the geotechnical report.
Worked example
Six round piers, each a 12 in tube 4 ft deep. How much concrete, and how many bags?
- Tube diameter12 in
- Depth4 ft
- Count6 piers
- Radius = 12 in ÷ 2 = 6 in = 0.5 ft. Volume each = π × 0.5² × 4 = 3.14 cu ft.
- Six piers = 3.14 × 6 = 18.85 cu ft (0.70 cu yd).
- At 0.6 cu ft per 80-lb bag: 18.85 ÷ 0.6 = 32 bags.
About 18.85 cu ft (0.70 cu yd) — 32 × 80-lb bags. Past ~1 cu yd, ready-mix usually beats bags on cost and time.
anvilfield.com/calculators/sonotube-pier-concrete-calculator · Free field calculators and FieldOS. A planning estimate, verify against the code, the manufacturer, and the engineer of record.
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Sonotube concrete FAQ
What is a footing?
A footing is the part of a foundation that bears directly on the soil and spreads a building's load over enough ground to keep the soil from overloading. A spread footing sits under a column, a strip footing under a wall. Its size comes from the load divided by the soil's allowable bearing capacity.
What is the difference between a shallow and a deep foundation?
A shallow foundation bears near the surface and spreads load into soil that is strong close to grade, using spread, strip, or mat footings. A deep foundation uses piles or drilled piers to carry the load down through weak soil to a firm layer. The soils report decides which the site needs.
How deep should a footing be?
A footing has to bear on firm soil, below the local frost line, and at least 12 in below undisturbed ground under the IBC and IRC. The frost line is regional, from about a foot in the south to 4 ft or more up north. A frost-protected shallow foundation can sit shallower with perimeter insulation.
What is a spread footing?
A spread footing, also called an isolated or pad footing, is a concrete pad under a column that spreads its point load over the soil. Its plan area is the service load divided by the allowable bearing pressure, and its thickness and bottom steel are sized for shear and bending under ACI 318.
How big does a footing need to be?
A footing's bearing area is the service load divided by the soil's allowable bearing capacity. A 60,000 lb column on 3,000 psf soil needs about 20 square feet, so roughly a 4 ft 6 in square pad. The soils report sets the bearing value, and the engineer sets the thickness and reinforcement.