Sonotube Concrete Calculator
Bags of concrete to fill any sonotube column
What is sonotube concrete calculator?
A sonotube concrete calculator sizes the cubic yards and bag count for sonotube columns — cardboard tube forms used for cylindrical concrete piers. Sonotube is a brand name (Sonoco) but the term is generic; Quik-Tube and Lowes-brand tubes work identically. The volume math is π × r² × h, where r is half the diameter.
Standard sizes. Sonotubes come in 8, 10, 12, 14, 16, and 24 in diameters. For residential decks, 10-12 in is the workhorse. Mailboxes and sign posts use 8 in. Porch columns and pier foundations use 14-16 in. The 24 in size is for commercial work.
Depth = frost line + bigfoot. A sonotube needs to extend below the local frost line so winter heaving doesn’t lift the deck. Add roughly 12 in extra so the bigfoot pad (the wider concrete pad at the base of the column) also sits below frost. In a 36 in frost region, plan on a 4 ft sonotube sitting on an 18 × 18 × 8 in bigfoot pad. Total dig depth: about 4.5-5 ft.
Why a bigfoot pad matters. A 10 in sonotube has 0.55 ft² of contact with the soil. Under a 5,000 lb deck load, that’s 9,000 PSF of bearing stress — exceeds most soils. The 18 × 18 in bigfoot pad is 2.25 ft² of contact, dropping the bearing stress to 2,200 PSF — well within typical clay/loam capacity. Without the pad, the column edge cuts into the soil under load.
Common volumes (calculator output for reference):
- 8 in × 4 ft: 0.05 cu yd / 3 bags
- 10 in × 4 ft: 0.08 cu yd / 4 bags
- 12 in × 4 ft: 0.12 cu yd / 6 bags
- 16 in × 4 ft: 0.21 cu yd / 10 bags
Pour tips. Most sonotube pours are under 1 cu yd, so bagged premixed concrete is the right product. Quikrete Fast-Setting or Sakrete Fast-Setting lets you backfill same-day. Always vibrate or rod the concrete to eliminate voids — air pockets in a 4 ft column compromise structural strength.
When to use a sonotube concrete calculator
- Deck pier — 10 or 12 in sonotube extending below the frost line, sitting on a bigfoot pad. Most residential decks use 4-8 piers; this calculator sizes one — multiply by count.
- Porch column — Decorative column wraps a structural sonotube. 12-16 in tubes are common; the calculator handles the volume math for any diameter.
- Mailbox or sign post — Smaller sonotube (8 in) for fence-line mailboxes and sign posts. 30-36 in below grade is standard. About 4 of 80-lb bags per post.
How to use the Sonotube Concrete Calculator
- Pick the sonotube size — Common diameters: 8, 10, 12, 14, 16 in. For deck piers, 10-12 in is standard. For heavier loads or porch columns, 14-16 in. Check IRC R407 for required sizes.
- Measure the depth — Sonotube depth = frost line depth + ~12 in for the bigfoot pad below it. In a 36 in frost line region, plan on a 4 ft sonotube + an 18 × 18 × 8 in bigfoot pad below.
- Enter dimensions in the Column tab — The calculator defaults to the Cylinder shape. Diameter in inches, height in feet. Output is cubic yards plus a bag count for the tube alone.
- Add the bigfoot volume separately — Switch to the Footing tab and enter the bigfoot pad dimensions (e.g. 18 × 18 × 8 in). Add to the sonotube total for the full pier volume.
Worked examples
8 in × 4 ft
Input: Column tab: 8 in dia × 4 ft
Output: 0.05 cu yd / 3 of 80-lb bags10 in × 4 ft
Input: Column tab: 10 in dia × 4 ft
Output: 0.08 cu yd / 4 of 80-lb bags12 in × 4 ft
Input: Column tab: 12 in dia × 4 ft
Output: 0.12 cu yd / 6 of 80-lb bags