How to use this calculator
- Enter footing geometry. Use round footing diameter and concrete depth.
- Enter count. Use the number of identical footings in the deck layout.
- Set bag yield. Use the concrete volume produced by one bag.
- Read the takeoff. Use total volume, bags to buy and concrete weight as a material estimate.
How it works
This deck footing concrete calculator treats each footing as a round cylinder:
V_one = pi x (D / 2)^2 x h
Total volume multiplies by the footing count, then bag count rounds up from the entered bag yield:
V_total = V_one x N
bags = ceil(V_total / bag_yield)
Concrete weight is estimated from density:
weight = V_total x density
Worked example
Verified against the live calculator
Six 12 in diameter by 48 in deep round footings need
about 18.8 ft^3 of concrete. With 0.6 ft^3 per bag,
the takeoff rounds up to 32 bags. At normal-weight concrete
density, that is about 2700 lb of concrete.
Frequently asked questions
How do you calculate concrete for round deck footings?
Use the cylinder volume formula: volume = pi x (diameter / 2)^2 x depth. Multiply by footing count, then divide by bag yield and round up.
Does this size the deck footing?
No. It only estimates concrete quantity. Footing diameter, depth, rebar, post base and frost/bearing requirements still need local code, soil and design review.
What bag yield should I enter?
Use the yield printed on the bag or product datasheet. A common 80 lb premix bag is about 0.6 cubic feet, but products vary.
Should I add waste?
Yes. Add extra bags for over-excavation, irregular holes, bell bottoms, tube gaps, spillage and partially filled bags.
Method & assumptions
- Round cylindrical footings only. Square pads, spread footings, bells and stepped holes need separate volume math.
- Bag count is rounded up before any project waste allowance.
- This is not a structural or code calculator. It does not choose footing size, frost depth, bearing area, uplift resistance, post bases, rebar or lateral bracing.
- Use deck board takeoff, wood beam span and board feet for adjacent planning checks.