Sonotube Calculator — Concrete Volume
Calculate how many bags of concrete mix you need to fill sonotube forms for deck post footings and piers. Enter tube diameter, depth, and the number of tubes to get an instant bag count.
Enter Dimensions
Depth below grade to bottom of footing
Results
Bags per Tube
5bags
Total Bags
20bags
Volume per Tube
2.18cu ft
Concrete volume for one tube
Total Volume
0.323cu yd
All tubes combined
Editorial Standards
Each calculator is reviewed for formula accuracy, unit consistency, and alignment with current U.S. building practices before publication. We verify outputs against published engineering references and real-world project data. Learn more about our methodology.
Any post that needs to bear below the frost line gets a sonotube footing — deck posts, pergola columns, gate posts. The tubes are cheap; the concrete is what adds up. Bag count depends on tube diameter, how deep you pour, and what bag size you buy.
Quikrete and SAKRETE publish bag yields: 0.30 cu ft per 40 lb bag, 0.45 cu ft per 60 lb, 0.60 cu ft per 80 lb. Common tube diameters run 8–16 inches. Pour depth has to clear the local frost line — 36–48 inches in the northern U.S., shallower farther south. Every tube takes the same bag count, so total bags are just bags-per-tube times the number of footings.
Specialized Versions
How the Sonotube Calculator Works
The calculator treats each sonotube as a cylinder: volume = π × r² × depth. The radius is half the tube diameter converted to feet. Dividing the volume by the yield per bag (0.30 cu ft for 40 lb, 0.45 cu ft for 60 lb, 0.60 cu ft for 80 lb) and rounding up gives the bags per tube. Multiply by tube count for the project total.
If your project includes a concrete slab or pad in addition to the footings, use the Concrete Slab Calculator to estimate cubic yards and bag counts for the flat pour.
Concrete Bag Reference (60 lb Bags, 4-Foot Depth)
| Tube Diameter | Depth | Volume (cu ft) | Bags (60 lb) |
|---|---|---|---|
| 6 in | 4 ft | 0.79 | 2 |
| 8 in | 4 ft | 1.40 | 4 |
| 10 in | 4 ft | 2.18 | 5 |
| 12 in | 4 ft | 3.14 | 7 |
Bag yields per Quikrete published data: 40 lb = 0.30 cu ft, 60 lb = 0.45 cu ft, 80 lb = 0.60 cu ft. Always round up — partial bags cannot be stored once mixed.
Pro Tips
- Cut tubes 2 inches above grade. Leave sonotube forms 2 inches above the finished grade so the post base sits above the soil-water interface. This reduces moisture contact at the post-concrete joint, the most common failure point in deck footings.
- Use fast-setting concrete to save time. Quikrete Fast-Setting or SAKRETE Fast-Setting can be poured dry into the wet hole with water added on top. No mixing is required, the tube is ready to load in 20–40 minutes, and it reaches full strength within 24 hours.
- Plumb and brace the post before the concrete sets. Once you fill the tube, check the post with a level on two adjacent faces and use diagonal bracing to hold it in position. Fast-setting concrete locks the post angle in place within minutes — there is little time to correct after pouring.
- Verify frost line depth before setting tube depth. Frost line depth varies by location — 12 inches in southern states, up to 60 inches in northern Minnesota. The bottom of the tube must be at or below the local frost line or the footing will heave seasonally.
Common Mistakes
- Using too small a tube diameter. A 6-inch tube works for a light pergola post but is undersized for a deck beam post that carries heavy live and dead loads. Check your structural drawings or consult a building inspector before choosing tube diameter.
- Adding water to dry fast-setting mix before placing. Fast-setting concrete is designed to be poured dry and activated with water in the hole. Mixing it in a bucket before placing defeats the purpose and reduces workability.
- Stopping the pour short of the tube top. A partial fill leaves the post embedment depth shorter than designed. Always fill to the top of the tube (or to the target grade), and confirm depth with a tape measure before the concrete sets.
Tube Size, Frost Line, and Load Guidance
Choosing Tube Diameter by Load
IRC Table R507.3 provides maximum post-to-beam spans, but footing diameter ultimately depends on soil bearing capacity and tributary area. The table below covers typical residential deck footings using 2,000 psf soil bearing (average residential soil):
| Tube Diameter | Typical Use | Max Tributary Area (2,000 psf soil) |
|---|---|---|
| 6 in | Light pergola, mailbox, sign post | ~16 sq ft |
| 8 in | Residential deck post (small deck) | ~32 sq ft |
| 10 in | Standard deck post, shed corner | ~50 sq ft |
| 12 in | Larger deck, beam post, heavy load | ~72 sq ft |
| 16 in | Structural column, large beam support | ~128 sq ft |
For any permitted deck, a structural engineer or your local building department should verify footing size against actual soil conditions and live/dead load calculations.
Frost Line Depth by Region (USA)
The bottom of every footing must reach below the local frost line to prevent seasonal heaving. Frost depth varies significantly across the country:
| Region | Example States/Cities | Typical Frost Depth |
|---|---|---|
| Deep South / Southwest | FL, LA, AZ, southern TX | 0–12 in |
| Mid-Atlantic / Pacific Coast | VA, NC, OR, WA coast | 12–24 in |
| Midwest / Mountain West | OH, IN, CO, UT | 24–36 in |
| Northern States | IL, PA, NY, WI, MI | 36–48 in |
| Deep North | MN, ND, northern ME | 48–60 in |
These are guidelines only — always confirm the required frost depth with your local building department before pulling a permit.
Sonotube / Quik-Tube Material Pricing (2025–2026)
Cylindrical concrete forms are sold under two common brand names: Sonotube (Sonoco) and Quikrete Quik-Tube. Both are available at major home improvement retailers. Prices below are for standard 4-foot lengths:
| Diameter | Length | Retail Price | Notes |
|---|---|---|---|
| 8 in | 4 ft | ~$9–$12 | Quikrete Quik-Tube #692201; Ace Hardware $9.59 |
| 10 in | 4 ft | ~$14–$18 | Quikrete Quik-Tube #692202 |
| 12 in | 4 ft | ~$18–$25 | Quikrete Quik-Tube #692203; HD/Lowe's retail |
| 12 in | 12 ft | ~$48–$80 | Sonotube brand; Menards / specialty suppliers |
| 16 in | 4 ft | ~$35–$55 | Less common at retail; order through building supply |
Tube prices are secondary to concrete bag costs for most projects. One 8-inch × 4-foot pour at 4-foot depth requires roughly 5 bags of 60 lb mix (~$30–$40 in concrete), making the tube itself a minor fraction of total material cost.
Frequently Asked Questions
How much concrete do I need for a sonotube?
A 10-inch tube at 4 feet deep takes about 2.18 cubic feet — roughly 5 bags of 60 lb mix.
What size sonotube do I need for a deck post?
The footing diameter should be at least 3 times the post width. For a 4×4 post, use an 8-inch tube; for a 6×6 post, use a 10- or 12-inch tube. Always check local building codes — many jurisdictions specify minimum footing sizes for deck loads.
How deep should a sonotube footing be?
The bottom of the footing must be below the local frost depth to prevent heave. In northern U.S. climates this is typically 36–48 inches. In mild southern climates, 12–18 inches may suffice. Check your local building department for the required frost depth.
What concrete mix should I use for sonotubes?
Use a standard ready-mix bag such as Quikrete 5000 or SAKRETE High Strength Concrete Mix (at least 4,000 psi). For a standard residential deck footing, 3,000–4,000 psi concrete is sufficient. Mix to a stiff consistency — not soupy — to minimize shrinkage.
Do I need rebar in a sonotube?
For most residential deck footings, a single vertical #4 rebar centered in the tube is enough to meet code. For larger loads or engineer-specified footings, use multiple bars or a rebar cage. Always anchor the post base hardware before the concrete sets.
How long does sonotube concrete take to cure?
Ready-mix concrete in sonotubes typically reaches working strength in 24–48 hours and full strength (28-day cure) in about 4 weeks. Do not load the footing — set posts or beams — until at least 24 hours have passed in warm weather, or 72 hours in cool weather.