Round piers and belled bases
Concrete Pier & Caisson Calculator
Four straight 18-inch by 8-foot piers need about 2.30 cubic yards with 10% waste, or 104 common 80-lb bags. Calculate your approved shaft and bell dimensions, then check the order quantity and delivery costs.
Concrete pier calculator example
4 x 18 in x 8 ft = about 2.30 yd3
That is about 104 common 80-lb bags with 10% waste or a 2.5 yd3 rounded ready-mix planning order.
18 in shaft + 36 in bell
shaft and bell calculated separately
Enter straight shaft height above the bell so the tapered base is not counted twice.
Foundation handoff
volume first, quote scope second
Move the approved pier quantity into foundation cost review only after shaft, bell, waste, and delivery assumptions are visible.
Shaft, bell, bags, and ready-mix order
Enter only the straight shaft height above the bell. For an 8-foot total pier with a 1-foot bell, enter 7 feet of shaft and 12 inches of bell height. Turn the bell off for a straight pier.
Geometry map
Shaft height stops where the bell begins.
Per pier before waste
0.61 yd3
16.49 ft3 per approved detail.
Project with waste
2.69 yd3
2.05 m3 across 4 piers.
80-lb bags
121 bags
Uses 0.60 ft3 per bag; confirm the exact product yield.
Rounded ready-mix order
2.75 yd3
$481 at the entered price for this rounded quantity, before minimums and fees.
Material at the calculated volume with waste: $470. The rounded order above is a separate estimate. The example unit price is editable, not a local quote. Supplier minimums, delivery, short-load fees, pumping, testing, tax, and installation are extra.
Geometry boundary
49.48 ft3 shaft + 16.49 ft3 bell before waste.
Field overrun question
Ask how overbreak, cave-ins, casing, groundwater, pump waste, and unused concrete are measured and billed.
Design boundary
Use approved dimensions. This tool does not choose shaft depth, bell size, reinforcement, or bearing capacity.
Pier holes, concrete bags, and delivery minimums
Measure the space that will actually receive concrete. An open drilled hole uses its approved excavation dimensions; a form tube uses its inside diameter. If a post occupies the hole, use the concrete post hole calculator to subtract the post volume. A cylinder estimate does not select a safe pier diameter or depth.
| Approved geometry example | With waste | Bags | Rounded order |
|---|---|---|---|
| 4 straight piers: 18 in x 8 ft | 2.30 yd3 | 104 | 2.50 yd3 |
| 4 piers: 18 in x 7 ft shafts + 36 in x 12 in bells | 2.69 yd3 | 121 | 2.75 yd3 |
Bags are also a handling decision
The straight-pier example needs 104 bags, or 8,320 lb of dry mix. That excludes pallets, mixing water, equipment, and people. Check vehicle payload, unloading space, crew capacity, mixer output, and the required placement sequence. Bag count alone cannot tell you whether on-site mixing is practical.
Use the concrete bag calculator for other bag sizes and yields. Round up the combined batch once when piers share a pour; separately staged pours may need their own rounding and allowances.
Price the quantity you will be billed for
At an illustrative $175 per cubic yard, the 2.30-yard straight-pier calculation is about $403 in concrete. A 2.50-yard rounded order is $437.50 before fees. Neither amount is an installed price or a promise that a supplier will deliver that quantity.
Ask about minimum billable yards, delivery increments, short-load charges, unloading time, and leftover concrete. Compare the delivered totals in the delivery cost calculator before choosing bags, mini-mix, volumetric, or ready-mix.
Confirm the hole before dispatch
- Confirm shaft height, bell height, pier count, and cut-off elevation from the approved detail. Do not include the bell height twice.
- Separate measured overbreak from a general waste allowance. If the hole changes, agree on a revised quantity instead of adding another unexplained percentage.
- Ask the drilling contractor how casing, groundwater, cleanout, and inspection affect the placement plan. Standing water or unstable ground needs qualified review, not simply more concrete.
- Record who approves extra concrete, when to call for it, and how pump, waiting, testing, spoil removal, and returned material will be charged.
Interactive workflow
Run the numbers, then save or export the project
From pier volume to a supplier order
A clean volume answer is useful only when the dimensions mean the same thing on the drawing, in the hole, on the concrete ticket, and in the contractor quote.
One cylinder for every pier
- Replace with local input
- Separate the straight shaft from an approved belled base. Enter shaft height above the bell to avoid double-counting the tapered section.
- Next check
- Confirm shaft diameter, bell diameter, bell height, count, and tolerances from the approved detail.
Calculated volume equals ordered volume
- Replace with local input
- Keep waste, overbreak, irregular excavation, casing displacement, pump priming, testing, and supplier order increments visible.
- Next check
- Ask who owns concrete overrun and how unused or returned concrete is billed.
Pier and caisson are interchangeable
- Replace with local input
- Terminology varies by region and trade. The approved geometry, reinforcement, bearing detail, construction method, and inspection requirements control the work.
- Next check
- Use the project drawings and local professional language in the quote rather than relying on the label alone.
Pier and caisson quote checklist
Use these checks before comparing a per-pier price or approving a concrete quantity.
Approved geometry
The shaft diameter, straight height, bell dimensions, count, cut-off elevation, and concrete cover are stated.
Resolve missing dimensions with the designer or qualified local professional before ordering.
Excavation condition
Soil stability, casing or slurry, groundwater, rock, spoils, cave-in risk, overbreak, and cleanout responsibility are priced or excluded.
Ask how field overrun is measured and who approves a changed hole.
Reinforcement and embeds
Steel cage, dowels, anchor bolts, sleeves, templates, cover, chairs, lifting, and inspection timing are clear.
Keep steel and embed scope separate from concrete material volume.
Placement and testing
Truck or pump access, placement method, slump, testing, tremie needs, wait time, washout, and rejected-load responsibility are written.
Normalize delivery, pump, wait, and testing allowances across bids.
Structural boundary
The calculator has not been used to choose diameter, depth, bell size, bearing capacity, reinforcement, or load capacity.
Use approved drawings, geotechnical information, permits, and required inspections.
| Signal to check | What it means | Next step |
|---|---|---|
| Approved geometry | The shaft diameter, straight height, bell dimensions, count, cut-off elevation, and concrete cover are stated. | Resolve missing dimensions with the designer or qualified local professional before ordering. |
| Excavation condition | Soil stability, casing or slurry, groundwater, rock, spoils, cave-in risk, overbreak, and cleanout responsibility are priced or excluded. | Ask how field overrun is measured and who approves a changed hole. |
| Reinforcement and embeds | Steel cage, dowels, anchor bolts, sleeves, templates, cover, chairs, lifting, and inspection timing are clear. | Keep steel and embed scope separate from concrete material volume. |
| Placement and testing | Truck or pump access, placement method, slump, testing, tremie needs, wait time, washout, and rejected-load responsibility are written. | Normalize delivery, pump, wait, and testing allowances across bids. |
| Structural boundary | The calculator has not been used to choose diameter, depth, bell size, bearing capacity, reinforcement, or load capacity. | Use approved drawings, geotechnical information, permits, and required inspections. |
Related concrete planning tools
Move from a single calculation into a purchase, proposal, or pour-day decision with connected calculators and checklists.
How do I calculate concrete for a round pier or caisson?
For a straight shaft, multiply pi by radius squared by the straight shaft height, then multiply by the number of piers. Add the separate bell volume when the approved detail includes a belled base, then add waste before ordering.
Are concrete belled piers the same as caissons?
The terms can overlap in everyday construction language, but usage varies by region, contractor, and design discipline. Do not use the label to infer structural equivalence. Use the approved shaft, bell, reinforcement, bearing, construction, and inspection details for the project.
How is a belled pier volume calculated?
This calculator treats the bell as a conical frustum between the shaft diameter and bell diameter. Enter only the straight shaft height above the bell, then enter the bell height separately so the bell is not counted twice.
Does the calculator design the pier diameter or depth?
No. It estimates concrete material from dimensions you already have. Bearing capacity, loads, settlement, frost, uplift, lateral resistance, reinforcement, bell geometry, casing, and code compliance require qualified local design and review.
Why can ordered concrete exceed calculated pier volume?
Drilled excavations can have overbreak, irregular sides, groundwater, cave-ins, casing effects, pump or tremie waste, testing, and supplier order increments. Confirm the field-measurement and overrun rules before placement.
How many bags of concrete do four 18-inch piers need?
For four straight piers, each 18 inches in diameter and 8 feet tall, 10% waste gives about 62.20 cubic feet. At 0.60 cubic feet per 80-lb bag, round the combined total up to 104 bags. That is 8,320 lb of dry mix before water, pallets, tools, or people. Confirm product yield and delivery capacity before buying.
Does a 2.5-yard planning order meet the supplier minimum?
Not necessarily. Quarter-yard rounding is a planning convention in this calculator, not a supplier policy. A supplier may use different increments, charge a short-load fee, or bill a higher minimum quantity. Ask for the delivered total, minimum billable yards, unloading allowance, and any pump or returned-concrete charges.
Planning disclaimer
This pier and caisson calculator estimates material volume only. It does not design foundations or verify bearing capacity, loads, settlement, frost, uplift, reinforcement, casing, excavation safety, groundwater control, placement method, permits, inspections, or code compliance. Use approved drawings and qualified local professionals.