How this calc works

A Sonotube pour is a cylinder, so the volume is pi times the radius squared times the height — the same round-hole math that trips people up on post holes. This calc takes the tube diameter in inches and the height in feet, converts the diameter to a radius in feet, and returns cubic yards plus a bag-count estimate and 10% waste.

Diameter to radius is the step people drop: you divide the diameter by 24, not 12, because you are converting inches to feet and halving to a radius in one move. The calc handles it; the Show the Math view makes the conversion explicit so you can check it.

Common mistakes

The usual error is treating the tube as a box and overbuying, or dropping the inches-to-feet conversion on the diameter and being off by a factor of 12. Round columns are exactly where square-volume calculators fail.

The second is forgetting that several tubes add up fast. One 12-inch tube is a fraction of a yard, but a deck on a dozen piers crosses into truck territory — total them before you decide bags versus ready-mix.

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