Pier guide

Use the tube's inside diameter, then account for everything outside the cylinder

A Sonotube is easy to calculate when it is truly uniform. Bell bottoms, exposed holes, and overbreak are where the missing concrete usually hides.

Published June 12, 2026 · Updated June 15, 2026 · 6 minute read
Quick answer: Sonotube concrete volume = π × radius² × concrete height, measured from the tube's inside diameter. A 12-inch tube filled 4 feet high holds about 3.14 cubic feet, or 0.116 cubic yard before waste. Because radius is squared, moving from a 12- to a 16-inch diameter adds about 78 percent more concrete per foot of height. Flared bases and earth-formed sections below the tube are separate volumes.
Sonotube pier section showing a cylindrical form, concrete core, soil, and depth markers
Conceptual Sonotube section. Verify bearing depth, base detail, and connection hardware from the approved foundation detail.

The cylinder formula

Measure the form's inside diameter and the concrete height. Divide diameter by two to get radius. Keep units consistent before multiplying.

Round pier volume = π × radius² × concrete height

A 12-inch-diameter tube filled 4 feet high contains about 3.14 cubic feet, or 0.116 cubic yard before waste. Because radius is squared, diameter errors matter: increasing diameter from 12 to 16 inches increases cross-sectional area by about 78 percent.

Concrete height is not always hole depth

The tube may stop above a flared base, start below finished grade, or extend above grade. Use the total concrete geometry, not one convenient field measurement. Calculate enlarged bases, pads, or caps separately.

Earth-formed portions add uncertainty

An augered hole can be larger than the nominal bit size because of loose soil, rock removal, collapse, or cleanup. If concrete fills an open earth section below the tube, include that shape and choose a waste allowance that reflects overbreak. Do not assume the cardboard cylinder controls all concrete below grade.

Frost and bearing requirements control depth

Pier diameter, embedment, bearing, uplift, lateral resistance, spacing, and connection details are design decisions. The calculator's frost guidance reports an approximate state value but cannot tell how much of the entered pier height is buried. Verify local frost depth and the approved foundation detail.

Cage output is a takeoff, not a design

Pour Ready can estimate longitudinal bars and closed ties or a spiral from entered bar sizes, count, spacing, and cover. Those inputs must come from the plans or responsible professional. The tool checks basic geometric feasibility and stock-length quantities; it does not establish structural adequacy, development, splices, hooks, or connections.

Multiply identical piers carefully

Calculate one pier and multiply only when diameter, height, and base shape are identical. Group different sizes separately. For many small piers, consider cumulative placement loss, leftover concrete between batches, and whether bag mixing can maintain a consistent placement schedule.

Field check: record tube inside diameter, formed height, earth-formed height, and base geometry as four separate items before calculating.

Sources and further reading

Use this guide with the Pour Ready methodology page, the pier schedule for your project, and local frost-depth or deck-foundation requirements.