A round concrete pier starts with a cardboard form tube — $9 to $15 at the box store for a 4-foot length in the common sizes. Fill a 12-inch one four feet deep and you'll mix six 80-lb bags of concrete, about $36 at $6 a bag. Call it $50 per pier, DIY. A six-pier deck runs near $300 in tubes and concrete; past about a yard of total pour, ready-mix takes over and the math flips in your favor.
Sonotube is the brand that became the generic — the round fiber forms from Sonoco. Home Depot stocks the Quikrete QUIK-TUBE and Sakrete equivalents at friendlier prices, with genuine Sonotube at Menards and contractor supply counters running higher. All of them do the same job: hold a cylinder of wet concrete while it cures.
| Tube size | Volume per ft of depth | 80-lb bags per ft | 4-ft tube (box store) | Typical use |
|---|---|---|---|---|
| 8 in | 0.35 cu ft | 0.6 | $9-$14 | Fence posts, small signs |
| 10 in | 0.55 cu ft | 0.9 | $10-$15 | Light deck piers |
| 12 in | 0.79 cu ft | 1.3 | $13-$15 | Standard deck piers |
Prices shake out to roughly $3.50 per running foot for the 12-inch size. Frost-depth piers need longer stock: 10-foot lengths list around $20-$25 in 8-inch and $30-$40 in 12-inch, cut to your required depth. Fourteen- through 18-inch diameters are special order at most stores — the moment you need those, you're likely on an engineered plan anyway.
The volume is a cylinder: π × (diameter ÷ 2)² × depth. One 80-lb bag of premix yields about 0.60 cubic feet. Divide the first by the second and round up — you can't mix a fraction of a bag, and a pier that finishes 2 inches short is a redo.
| Pier | Concrete | 80-lb bags | Concrete @ $6/bag | Tube | DIY total |
|---|---|---|---|---|---|
| 8 in × 4 ft | 1.40 cu ft | 3 | $18 | $12 | $30 |
| 10 in × 4 ft | 2.18 cu ft | 4 | $24 | $13 | $37 |
| 12 in × 4 ft | 3.14 cu ft | 6 | $36 | $14 | $50 |
| 12 in × 6 ft (frost) | 4.71 cu ft | 8 | $48 | $21 | $69 |
Two adjustments from the field. First, add 5 to 10 percent for spillage, the domed top most builders pour above grade, and tube settlement — the table's bag counts already round up, but a 10 percent cushion on a multi-pier job is one extra batch, not one extra trip. Second, many crews drop a length of #4 rebar or a couple of short crossing bars into each pier before the pour; at $0.50 to $1.00 a pound it's pocket change, and our rebar cost guide prices it out.
One cubic yard equals 45 eighty-pound bags. At $6 a bag, that's $270 of bags against a ready-mix price typically in the $150-per-yard range — so bags lose on pure cost immediately, but ready-mix plants add short-load fees below about a yard, and a mixing crew can't hold pace past roughly a bag a minute. The crossover lands near one yard of total pour:
| Job | Total w/ 10% waste | Bags | Bag cost | Ready-mix @ $150/yd |
|---|---|---|---|---|
| 6 piers, 12 in × 4 ft | 0.70 yd³ | 35 | $210 | $115 |
| 12 piers, 12 in × 4 ft | 1.54 yd³ | 70 | $420 | $231 |
| 20 piers, 12 in × 4 ft | 2.56 yd³ | 116 | $696 | $384 |
Read the trend, not the dollar signs: below a yard the short-load fee roughly erases ready-mix's advantage, and bags let you pour four piers on Saturday and four on Sunday. At 20 piers, ready-mix nearly halves the concrete bill and saves a full day of shovel work. Bag prices run roughly $5.50 to $7 at big boxes — the table uses $6 — and pallet quantities sometimes unlock a discount worth asking about.
Volume per tube, total yards, 80-lb bag count, and ready-mix cost from diameter, depth, and pier count.
Sonotube Calculator →Budget roughly $50 for a 12-inch × 4-foot pier — a $14 tube plus six bags — and $30-$37 for the smaller diameters. A six-pier deck is about $300 in materials if you mix it yourself; a 20-pier job crosses two yards and belongs on a ready-mix truck. The sonotube calculator turns diameter, depth, and count into cubic yards, bags, and cost in one pass. For the flatwork around it, the concrete calculator sizes slabs and footings, and the rebar calculator prices the steel that goes inside either one. Building a fence instead? The fence cost guide covers post spacing and line-post economics.
A 4-foot Quikrete or Sakrete brand 12-inch tube runs $13-$15 at Home Depot — about $3.50 per foot. Genuine Sonotube brand tubes from contractor suppliers run higher, with marketplace listings around $35-$50. Ten-foot lengths for frost-depth piers list at $30-$40 in 12-inch.
At 4 feet deep: an 8-inch tube takes 3 eighty-pound bags, a 10-inch takes 4, and a 12-inch takes 5.2 bags — round to 6. The math is cylinder volume (π × radius² × height) divided by 0.60 cubic feet of yield per 80-lb bag.
Six 12-inch tubes 4 feet deep total about 18.8 cubic feet — 0.70 cubic yards with a 10 percent cushion. That's 35 eighty-pound bags (about $210 at $6 a bag) or a $115 ready-mix order, before any short-load fee the plant adds below one yard.
In frost climates, code typically requires the pier bottom at or below the local frost line, which runs from 12 inches in warm zones to 48 inches or more in the northern tier. Your building department sets the number — call before you dig, and call 811 first for buried utilities.
Yes — the tube is designed to stay in place below grade and slowly deteriorate there, which is fine. Cut or snap off the above-grade portion after the concrete cures if the pier will be exposed, and grade soil away from the cardboard so it isn't wicking water.