Concrete Footing Calculator
This concrete footing calculator estimates the concrete for strip footings, foundation footings, and fence-post holes. Enter one footing’s length, width, and depth, set how many identical footings you are pouring, and it totals the cubic yards and bags. It doubles as a post hole concrete calculator for deck and fence work.
How to use this calculator
- Enter the length, width, and depth of a single footing.
- Set the number of footings if you are pouring several identical ones.
- Add a waste allowance for over-dig and spillage.
- Read the total cubic yards or bag count for the whole job.
The formula
Each footing is a box: length × width × depth. Multiply by the number of footings and divide by 27 for cubic yards:
Cubic yards = (Length ft × Width ft × Depth ft × Count) ÷ 27
Worked example. A 20 ft strip footing 16 inches wide and 8 inches deep: 20 × 1.333 × 0.667 = 17.78 cubic feet, or 0.66 cubic yards. Two identical footings would total about 1.32 cubic yards before waste.
Frequently asked questions
How do I calculate concrete for footings?
Multiply each footing’s length × width × depth for its volume, then multiply by the number of identical footings. Enter the count in this calculator and it totals every footing at once.
How much concrete do I need per fence post?
A post in a 10 inch wide, 2 foot deep hole uses about 0.07 cubic yards (≈3 × 60 lb bags) before subtracting the post. Wider or deeper holes use proportionally more.
How deep should a footing be?
Footings must sit below the local frost line and on undisturbed soil — often 12 to 48 inches deep depending on your climate. Check your local building code for the required depth.
Should I subtract the post volume from the hole?
For accuracy, yes. A 4 × 4 post fills part of the hole, so subtracting it avoids over-ordering. The difference is small for one post but adds up across a long fence line.