Setting deck posts? Enter how many footings you need, the hole size and the depth. You get the concrete volume and the number of bags to buy.
Your shopping list
31Bags of concrete
18.14 cu ftConcrete volume
0.67 cu ydCubic yards
- Volume per footing2.75 cu ft
Bag yields are typical. Check the label on your bag. Extra of 10% is included.
How to use the Deck Footing and Concrete Calculator
- Count your posts. Each post needs one footing.
- Pick the hole diameter and type the hole depth. Use your local frost depth.
- Pick the bag size and read the number of bags.
The math behind it
Volume per footing = 3.14 x (diameter / 2)^2 x depth
Total = volume x footings x (1 + extra %)
Bags = total volume / bag yield, rounded up
A worked example
What we typed in
- Number of footings: 9
- Hole diameter: 12 in round
- Hole depth: 48 in
- Concrete bag size: 80 lb bag (about 0.6 cu ft)
- Extra for mistakes and cuts: 10%
What we got
- Bags of concrete: 52
- Concrete volume: 31.1 cu ft
- Cubic yards: 1.15 cu yd
- Volume per footing: 3.14 cu ft
Tips from the job site
- Dig below the frost line, or the footing can heave in winter.
- An 80 lb bag makes about 0.6 cu ft. Always check your bag label.
Common questions
How many bags of concrete for a deck footing?
A 12 in wide hole 42 in deep takes about 2.7 cu ft, or about 5 bags of 80 lb mix.
How deep should deck footings be?
Below your local frost line. It changes by region, so ask your building office.
See all Deck Calculators.
Last checked: (worked example and form display).