Concrete Calculator
Calculate concrete volume in cubic yards, cubic feet, and cubic metres, plus an estimated bag count, for slabs, footings, walls, and columns.
Estimate how much concrete you need — net volume, order quantity with allowance, and an estimated bag count — for slabs, footings, walls, and columns.
Extra concrete to cover spillage, subgrade variation, and minor measurement differences — not a guaranteed waste figure.
Bag yield varies by product. Check the yield printed on your bag or product data sheet.
Estimated Concrete
This estimates concrete quantity from the dimensions you supplied. It does not determine structural requirements, footing dimensions, slab thickness, reinforcement, concrete mix design, or code compliance.
Calculation breakdown
Net volume
Order allowance
Allowance
Estimated order
Bag estimate
Bag yield varies by product. Check the yield printed on your bag or product data sheet.
How to Calculate Concrete
- Measure the dimensions of each pour (length, width, thickness, depth, height, or diameter, depending on shape).
- Calculate each section's volume and add them together for the net volume.
- Add an order allowance to cover spillage, subgrade variation, and minor measurement differences.
- Convert to cubic yards for ready-mix ordering, or to a bag count for bagged concrete.
Concrete Volume Formula
- Slab / Pad: volume = length × width × thickness.
- Footing: volume = length × width × depth.
- Wall: volume = length × height × thickness.
- Round / Column: volume = π × (diameter ÷ 2)² × height.
1 cubic yard = 27 cubic feet.
How Many Bags of Concrete Do I Need?
Divide your estimated order volume (in cubic feet) by a single bag's yield, then round up — a partial bag still counts as a full bag. The calculator uses the ORDER volume (net volume plus allowance), not the raw net volume, for the bag estimate.
Concrete Bag Yields
Reference yields only — bag yield is product-specific. Check the yield printed on your bag or product data sheet.
| Bag size | Reference yield |
|---|---|
| 40 lb | 0.30 ft³ |
| 50 lb | 0.375 ft³ |
| 60 lb | 0.45 ft³ |
| 80 lb | 0.60 ft³ |
| 90 lb | 0.675 ft³ |
How Much Extra Concrete Should I Order?
A common order allowance is 5-15% to cover spillage, subgrade irregularities, and minor measurement variance — not a guaranteed waste figure. This calculator defaults to 10%, adjustable from 0% to a custom amount.
Ready-Mix vs Bagged Concrete
Small projects are often more practical with bagged concrete; larger pours are typically more economical and consistent with ready-mix delivery. Ready-mix suppliers may have minimum order quantities, delivery requirements, and ordering increments — confirm the final quantity with your supplier rather than treating this calculator's figure as the exact order.
Concrete Calculator for Different Shapes
This calculator supports slabs/pads, footings, walls, and round columns — the shapes most concrete pours are built from. Select a project type above and the relevant dimension fields appear automatically.
Irregular Concrete Projects
There is no single formula for a truly irregular area. Instead, divide the project into simpler sections that match the supported shapes above, calculate each independently using "+ Add section," and the calculator sums them into one total before applying the order allowance once.
Frequently Asked Questions
How do I calculate how much concrete I need?
Calculate the volume of each pour (length × width × thickness for a slab, or the equivalent formula for your shape), add them together, then add an order allowance to cover spillage, subgrade variation, and minor measurement differences.
How many cubic yards of concrete do I need?
Divide your total cubic feet by 27 (there are 27 cubic feet in a cubic yard). The calculator above does this automatically and shows both figures.
How many bags of concrete do I need?
Divide your estimated order volume (in cubic feet) by the yield of a single bag, then round up — a partial bag still counts as a full bag. Bag yield varies by product, so check the bag or product data sheet for the actual yield.
How many 80-lb bags are in a cubic yard?
An 80-lb bag commonly yields around 0.60 cubic feet, so roughly 45 bags per cubic yard (27 ÷ 0.60) — but this varies by product. Always confirm the yield printed on your specific bag.
How much extra concrete should I order?
A common order allowance is 5-15% to cover spillage, subgrade irregularities, and minor measurement variance. This calculator defaults to 10%, adjustable from 0% up to a custom amount.
What is the difference between cubic feet and cubic yards?
A cubic yard equals 27 cubic feet. Ready-mix concrete is typically ordered in cubic yards; bagged concrete yields are typically listed in cubic feet.
Can I calculate an irregular concrete area?
Yes — break the project into simpler sections (for example a slab plus a footing), calculate each independently using "+ Add section," and the calculator sums them into one total.
Should I use bags or ready-mix?
Small projects (a few cubic yards or less) are often more practical with bagged concrete; larger pours are typically more economical and consistent with ready-mix delivery. This calculator shows both estimates so you can compare.