Construction calculator

Concrete cylinder calculator

Find how much concrete you need for a cylindrical form — a sonotube, footing, pier, or round column. Enter the diameter and height, get cubic yards, bag count, and weight.

Project:

Diameter d Width across the form, e.g. a 12-inch sonotube

Height / depth h How deep or tall the pour is

Number of forms e.g. 4 fence posts or 6 deck footings

Wastage allowance % Common spillage and overfill buffer — 5–10% is typical

Bag size

Concrete needed 0.1222yd³

Cubic feet 3.299ft³

Cubic meters 0.0934m³

Bags needed 8bags

Estimated weight 478lb

V = π × (d/2)² × h, then ÷ 1728 → ft³, ÷ 27 → yd³

How to calculate concrete for a cylindrical form

Sonotubes, round footings, deck piers, and fence posts are all cylinders, so the same volume formula applies — you're just usually working in inches and feet, and converting to cubic yards because that's how ready-mix concrete is sold.

V = π × (d/2)² × h

Where d is the diameter of the form and h is the depth or height of the pour. If your measurements are in inches, the result comes out in cubic inches — divide by 1,728 to get cubic feet, then by 27 to get cubic yards (since 1 yd³ = 27 ft³).

Worked example

A 12-inch diameter sonotube, 4 feet (48 inches) deep:

V = π × (12/2)² × 48 = π × 36 × 48 = 5,429.6 in³

5,429.6 ÷ 1,728 = 3.14 ft³

3.14 ÷ 27 = 0.116 yd³ — round up and order 0.15 yd³ to allow for spillage.

How many bags of concrete do I need?

Bagged concrete is sold by weight, but what matters for your pour is the cured volume each bag yields:

Bag size	Approximate yield
40 lb bag	≈ 0.30 ft³
60 lb bag	≈ 0.45 ft³
80 lb bag	≈ 0.60 ft³

Divide your required cubic feet by the bag's yield, then round up — concrete that's mixed slightly dry is better than running short mid-pour.

Multiple forms — fence posts, deck footings, columns

If you're pouring several identical forms, calculate the volume for one, multiply by the number of forms, then add your wastage allowance. The calculator above handles this with the "multiple forms" mode — useful for a row of fence posts or a full set of deck footings in one estimate.

Test cylinders for compressive strength

If you're casting concrete test cylinders for lab compressive-strength testing (commonly 4×8 inch or 6×12 inch cylinders per ASTM C39), the same volume formula applies — you're just working at a much smaller scale, usually in fractions of a cubic foot per cylinder rather than cubic yards.

Estimating weight

Normal-weight concrete weighs approximately 145 lb per cubic foot once cured. Multiply your cubic feet by 145 to estimate the total weight — useful for understanding load on forms, transport, or structural calculations.

Frequently asked questions

How much concrete do I need for a 12 inch sonotube?+

It depends on the depth. For a 12-inch diameter tube 4 feet deep, you need about 0.116 cubic yards (roughly 6 bags of 60 lb concrete). Enter your exact depth in the calculator above for a precise number.

How do I convert cubic feet of concrete to cubic yards?+

Divide cubic feet by 27, since there are 27 cubic feet in one cubic yard. This is the standard unit ready-mix concrete is ordered in.

How many 80 lb bags of concrete do I need per cubic yard?+

An 80 lb bag yields about 0.60 cubic feet, so you'd need roughly 45 bags to make one cubic yard (27 ÷ 0.60 ≈ 45). For smaller pours like sonotubes, the calculator above gives you the exact bag count for your specific dimensions.

How much does a cubic yard of concrete weigh?+

Normal-weight concrete weighs roughly 4,050 lb per cubic yard (about 145 lb per cubic foot, × 27 cubic feet).

Should I add extra concrete for wastage?+

Yes — a 5 to 10% buffer is standard practice to account for spillage, uneven ground, and minor overfill. The calculator includes this as an adjustable field.