Footing calculator
Concrete footing
calculator
Three footing shapes, one calculator. Size round piers poured in cardboard form tubes, bell-bottom footings that flare at the base, or a continuous strip footing under a wall — each in cubic yards, bags and whole form tubes.
Enter measurements ↓Optional
What will it cost?
Every material the calculator worked out gets its own price. Each field starts at a typical US figure so you have something to work from — change any of them to what your own supplier charges.
These prices are approximate. They are national US retail figures, and what you actually pay varies with your region, your supplier, the season and how much you buy at once. Treat them as a starting point, not a quote — always price the job from your own supplier's current figures before you order.
Your prices
More in this series
Put these figures to work
Sizing one part of a pour is easier when the slab itself is settled. Start with the main estimate, then come back for the detail.
- Concrete Calculator Concrete volume, ready-mix bags, gravel base and rebar
- Rebar Calculator Grid bars, lap splices, tie wire and steel weight
- Post Hole Concrete Calculator Concrete per hole, bags, gravel base and total yards
- Fence Calculator Posts, rails, pickets or rolls, gates, and concrete per post with bags, by fence style and height
- Concrete Steps Calculator Stepped volume, landing slab, bags and cubic yards
- Self-Leveling Compound Calculator Underlayment bags, average depth, primer and coverage
- Concrete Removal Cost Calculator Debris weight, dumpsters and demolition cost
- Concrete Bag Yields and Mix Ratios Bag yields, mix proportions and strength classes in one table
- Self-Leveling Concrete Thickness Minimum and maximum pour depth, gravel fills, and bags per 100 sq ft by thickness
- Concrete Curing and Drying Times When you can walk, load and drive on new concrete, how temperature changes it, and how long mortar takes
- Concrete Weight per Cubic Foot and Yard What a cubic foot, a cubic yard and a slab of concrete weigh, by type and thickness, and what a truck carries
- Fence Post Depth, Spacing and Sizes How deep to set a fence post by fence height, how far apart posts go by style, 4×4 or 6×6, bags of concrete per post, and how long each wood lasts
Tools for the job
What makes this job easier
Tools and materials that suit this kind of job. These are affiliate links: if you buy through one, Renovimo may earn a commission at no extra cost to you. It never changes the figures on this page.
Dovoh
Outdoor laser level with receiver
The receiver finds the beam in full sun, so you can set forms, footings and base to grade alone.
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Garvee
Two-wheel wheelbarrow
Stable on two wheels for bagged concrete, block and soil.
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Garvee
Stainless post base, 4-pack
Lifts a 4×4 off the concrete so the end grain stays dry.
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Garvee
Electric rebar cutter, up to #6
Cuts slab and footing bar to length in seconds, with no sparks.
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Garvee
Electric rebar bender, up to 5/8 in
Bends corner and hook bars for footings and walls in one stroke.
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Garvee
Folding platform truck, 1300 lb
Moves stacks of bags, block and brick without a wheelbarrow tipping.
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Not the tool you were after? Browse the whole range at Dovoh or Garvee — the stores these picks come from.
Based on your result
What you'll need
Quantities update after every calculation. Tubes are counted whole, because a pier is never spliced across two of them.
- Ready-mix concrete
- Bags to fill every footing
- Calculate above
- Form tubes
- Cardboard tubes cut to your depth
- —
- Rebar or dowels
- Vertical cage tying the footing to what sits on it
- —
- Post bases and bolts Amazon
- Anchors set while the concrete is wet
- As needed
As an Amazon Associate I earn from qualifying purchases.
The maths
How this concrete footing calculator sizes a pour
A pier is a cylinder and a strip footing is a trench, both straightforward. A bell footing is the one that catches people out: the flared base is a truncated cone, not a wider cylinder and not an average of the two ends.
bell = (bell height ÷ 3) × (A_top + A_base + √(A_top × A_base))
strip = length ft × (width in ÷ 12) × (depth in ÷ 12)
tubes = ⌈ count ÷ ⌊ tube length ÷ depth ⌋ ⌉
Sonotube and other cardboard form tubes
Form tubes come in 4, 8 and 12 foot lengths and in diameters from 6 to 24 inches. Cut them to depth with a handsaw, brace the top square before pouring so the shaft does not drift, and strip the cardboard above grade once the concrete has set.
Drilled piers: the same cylinder, without the tube
A drilled pier is augered and poured straight into the hole, so use this as a drilled pier calculator by choosing a round pier and entering the auger diameter. Ordering is the one thing that changes: an unlined hole is never quite true, so set the waste allowance to 10 or 15 percent rather than the 5 percent a smooth tube needs.
Footer or footing?
The same thing. "Footer" is the everyday word on many job sites and "footing" is the one on drawings, so a footer calculator and a footing calculator do the same sum. Choose a strip footing for a wall footer and a pier or a bell for a post.
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01
Pick the shape
A deck sits on piers, a heavier load or soft ground gets a bell, and a wall gets a continuous strip footing.
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02
A bell is a cone, not a cylinder
The flare is a truncated cone. Averaging the two diameters undercounts it by about 4%, and averaging the two areas overcounts by about 7%.
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03
Depth is set by frost, not by load
A footing that stops above the frost line will be lifted by the ground every winter, no matter how wide it is.
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04
Tubes are cut, not divided
A 12-foot tube gives three 48-inch piers, not 3.6, so the count rounds down before the tube count rounds up.
Worked example
Concrete for a set of deck piers
A 12 × 16 ft deck on a three-by-four post grid needs twelve footings. Take them at 10 inches across and 42 inches deep, a common frost depth through much of the middle of the country:
- 1. One pier — π × (10 ÷ 2 ÷ 12)² × 3.5 ft = 1.91 cubic feet
- 2. Twelve piers + 10 % — 1.91 × 12 × 1.1 = 25.2 cubic feet, or 0.93 cubic yards
- 3. Bags — 25.2 ÷ 0.60 ft³ per 80 lb bag = 42 bags
- 4. Form tubes — three 42 in piers come out of each 12 ft tube, so 4 tubes
Forty-two bags is a pallet and a half and more than 3 000 lb to lift, mix and pour by hand. That is the point to price a short load of ready-mix instead: just under a yard is small for a truck, and many plants add a short-load fee, but spread over twelve holes it often costs less than the bags and a mixer hire — and every pier comes from the same batch. The bag yields behind step 3 are in concrete mix and bag yields.
Pier spacing and size start with the deck
How many footings a deck has, and how far apart they go, is decided by the beam span, not the concrete. Wider spacing means fewer holes but a bigger load on each one, so the footing has to grow to spread it — deck footing sizes and spacing works through that trade-off by soil type and tributary area. Once the layout is fixed, enter the diameter, depth and count here.
Footings or post holes?
A footing carries a load on top of it: the post stands on a bracket at the surface of the concrete. A fence or mailbox post is set the other way, down into the hole with concrete or gravel packed around it, and the volume is the hole minus the post. For those, the post hole calculator takes the post size off the volume and counts bags per hole.
Good to know
Footing questions, answered
Below the frost line, which is 12 inches in the warm South and past 48 inches in the northern states. Depth is set by frost heave rather than by the weight of the deck, and a shallow footing will be pushed up every winter.
Eight to twelve inches carries most residential deck posts. Wider footings spread the load over soft ground; the span tables in your local code give the figure that matters.
The flared base spreads the load over more soil without widening the whole shaft, so you dig and pour less concrete than a full-width pier. It also resists uplift, which matters for decks and fences in wind.
Divide the tube length by the pier depth and round down. A 12-foot tube gives three 48-inch piers with a foot left over — and that offcut is not long enough to be a fourth.
Piers usually take two to four vertical bars tied into a small cage, or at minimum a dowel to connect the footing to what sits on it. Strip footings normally run two continuous bars near the bottom.
In firm, self-supporting soil, yes, and it is common for strip footings. A form tube gives a clean round shaft, a known volume and a smooth face above grade, which is why piers usually get one.
About 0.79 cubic feet per foot of depth, so a 48-inch pier is roughly 3.1 cubic feet — six 80 lb bags. Six of them is close to 0.7 of a cubic yard, which is where ready-mix starts to make sense.
Yes. Footer is the everyday word on many sites and footing the one on drawings. A wall footer is a strip footing; a footer under a post is a pier or a bell.
The same way as a form-tube pier: pi times the radius squared times the depth, with the auger diameter as the diameter. Allow 10 to 15 percent extra rather than 5, because an unlined hole is never perfectly round or smooth.