Sonotube Concrete Calculator

Updated 2026-05-16

Estimate concrete bags for cylindrical tube forms.

Quick estimate: 24 bags for 4 holes at 12 in diameter, 4 ft deep, 0.6 cu ft yield per bag, and 10% waste.

How much concrete for a round form?

Round concrete forms are calculated as cylinders. Use inside diameter, height or depth, and count, then convert the total volume to cubic yards or bags.

Diameter has a big effect

Cylinder volume uses radius squared, so a small increase in diameter can noticeably increase concrete quantity. Measure the inside diameter of the form or hole.

Tubes, piers, columns, and holes

Tube forms, piers, columns, and round holes use similar volume math, but their structural requirements can be very different. This page estimates material quantity only.

Before you calculate

  • Use the yield printed on the bag you plan to buy, because 40 lb, 50 lb, 60 lb, and 80 lb products can differ.
  • Measure project area and thickness before converting the volume into bags.
  • Keep waste visible for over-excavation, uneven base, mixing loss, and final top-off.

Common mistakes

  • Assuming every bag yields the same cubic feet.
  • Buying by bag weight without checking volume yield.
  • Forgetting that the final answer must round up to whole bags.

Formula

bags = ceil((holeCount * pi * (diameter / 24)^2 * depth * (1 + wastePercent / 100)) / yieldPerBag)

Assumptions

  • Tube diameter is entered as hole diameter.
  • Depth is entered in feet.
  • Use actual tube dimensions before ordering.

Example

Estimated concrete bags needed: 24 bags

How to use this calculator

  1. Enter post holes in count.
  2. Enter hole diameter in in.
  3. Enter hole depth in ft.
  4. Enter yield per bag in cu ft.
  5. Enter waste in %.
  6. Review the live estimate and compare it with the example result.
  7. Check the formula, assumptions, product labels, and site conditions before using the Sonotube Concrete Calculator result to plan materials.

Before you buy materials

  • Round up to full bags and compare the total bag count with ready-mix if the quantity gets large.
  • Check the product label for yield, water instructions, working time, and intended use.

FAQ

How many bags do I need for sonotube concrete?

Use hole diameter, hole depth, post count, bag yield, and waste, then round up to the buying unit when the result is sold as whole items. In the default example, the result is 24 bags.

How do I calculate concrete for a sonotube or tube form?

Calculate the cylinder volume from diameter and height, multiply by count, add waste, then convert to cubic yards or bags.

Do I use inside or outside diameter?

Use inside diameter because that is the space the concrete fills.

How do I calculate multiple piers?

Calculate one pier, then multiply by the number of identical piers. Calculate different pier sizes separately.

Does this design a structural pier or column?

No. It estimates concrete quantity only. Structural sizing and reinforcement require qualified guidance.

Related calculators

This calculator is for planning estimates only. Verify final quantities with product labels, project conditions, and a qualified professional when accuracy matters.