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Concrete · Columns & Piers

Concrete Column Calculator

Deck piers, fence-post footings, porch columns and structural piers — round or square, one or a hundred. Results include per-column volume so you can plan the mixing.

MaterialsCalc Editorial TeamMaterialsCalc Editorial TeamConstruction Estimating EditorsJuly 15, 2026

Concrete Column Calculator

Round (sonotube) and square columns or piers. Calculates one size, multiplied by the count you need.

Common sonotube sizes: 8, 10, 12, 16, 24 in.

Include the below-grade portion for deck piers.

Round vs square: the volume formulas

Round column

V = (π × d² ÷ 4) × h

d
inside diameter of the tube
h
column height
Square column

V = s² × h

s
side width
h
column height

Use the tube's inside diameter — a "12-inch" sonotube is 12 in inside. For belled piers (widened base for uplift or bearing), add a truncated cone: roughly one-third the bell height times the sum of the top area, bottom area and their geometric mean. In practice, adding one extra 80 lb bag per bell covers it.

Sonotube quick-reference table

Bag counts include ~5% waste, rounded up. One 80 lb bag yields 0.60 ft³.
Tube diameterVolume per ft of height80 lb bags per 4 ft pier
8 in (203 mm)0.35 ft³ / ft3 bags
10 in (254 mm)0.55 ft³ / ft4 bags
12 in (305 mm)0.79 ft³ / ft6 bags
16 in (406 mm)1.40 ft³ / ft10 bags
24 in (610 mm)3.14 ft³ / ft21 bags

Worked example: 9-pier deck foundation

Worked example

A 16 × 20 ft deck on nine 12 in sonotubes, each 48 in deep to reach frost depth.

  1. 1

    Section area of one tube

    π × 1² ÷ 4 = 0.785 ft²

  2. 2

    Volume per pier

    0.785 × 4 = 3.14 ft³

  3. 3

    All nine piers

    3.14 × 9 = 28.3 ft³

  4. 4

    Add 5% tube-form waste

    28.3 × 1.05 = 29.7 ft³ (1.1 yd³)

  5. 5

    As 80 lb bags

    29.7 ÷ 0.60 = 49.5 → 50 bags

Result: 50 bags of 80 lb mix, or 1.25 yd³ short-load ready-mix — price both.

Placement tips that prevent honeycombing

Frequently asked questions

Piers plus a slab or footing?

Run each element through its calculator, then combine the order — one truck is cheaper than two.

Concrete Calculator

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Sources & references

  1. [1]ACI 318-19: Building Code Requirements for Structural Concrete — American Concrete Institute, 2019
  2. [2]IS 456:2000 — Plain and Reinforced Concrete: Code of Practice — Bureau of Indian Standards, 2000
  3. [3]Design and Control of Concrete Mixtures, 17th ed. — Portland Cement Association, 2021