Concrete Footing Calculator

Six posts set in 10 in holes, 24 in deep, need about 11 bags of 80 lb concrete mix around 4x4 posts — enter your post count and hole size to get a bag count rounded up to what you can buy.

Number of posts

Hole diameter (in)

Hole depth (in)

Post size (4x4 = 3.5, 6x6 = 5.5, none = 0) (in)

Bag yield (ft³/bag)

Waste margin (%)

Volume per hole

0.93 ft³

Total volume

6.08 ft³

Bags

Concrete mix
11 bags
per bag for Concrete mix

Enter your local prices to see an estimated cost.

How we calculate this

Volume per hole = (π × (diameter ÷ 2)² − post width²) × depth, converted from cubic inches to cubic feet — the post takes up part of the hole, so we subtract it (3.5 in for a 4x4 by default). We multiply by your post count, add your waste margin (10% by default), then divide by your bag's cured yield (0.6 ft³ for an 80 lb bag, 0.45 ft³ for a 60 lb bag) and round up.

Estimates only. Check local codes and product labels. Read our full disclaimer.