How to use the concrete calculator
- Pick the shape. Each part of the job is a card: a slab (patio, shed base, path), a footing (the strip under a wall), a wall, a round column or tube, post holes or a flight of steps. Add a card for every part, and set How many when several are the same, like 12 fence post holes or 4 deck footings.
- Measure. Long sizes in feet (or metres), thicknesses, diameters and depths in inches (or centimetres). You can type other units too:
12'6",3.5 m,10 cm,4 in. - Pick the bag. The list has the common sizes of Quikrete, Sakrete and Easy Mix concrete with the yield each maker publishes (Sakrete's 25 and 30 kg bags are sold in Canada, Easy Mix in Australia). For another product, choose Another bag and type the yield printed on it.
- Set the extra. The calculator adds 10% for waste. Change it if you're sure of your base and forms.
Reading the result
The big number is the whole bags to buy, rounded up. Under it you see the volume to order with the extra included, the volume of each part, and the same concrete counted in other common bag sizes, so you can compare a stack of 40 lb bags you can lift easily with fewer 80 lb ones. The weight line is there because it surprises people: a cubic yard of bagged mix is 45 bags of 80 lb, 3,600 lb in all.
For ready-mix, use the volume line. Concrete trucks are ordered by the cubic yard or cubic metre, and the National Ready Mixed Concrete Association (NRMCA, CIP 31) advises ordering 4% to 10% more than the volume worked out from the plan, and notes that a truck mixer carries 8 to 12 cubic yards (5 to 9 m³). Ask your supplier about the smallest load they deliver.
How each shape is worked out
- Slab and footing: length × width × thickness. A 10 × 10 ft slab 4 in thick is 33.3 cu ft, or 1.23 cu yd.
- Wall: length × height × thickness.
- Round column or tube: π × radius² × height. A 12 in tube 4 ft tall holds 3.14 cu ft.
- Post holes: the hole's circle minus the post's square (or circle), × the depth of concrete. Set the depth to where the concrete stops, not the bottom of the post.
- Steps: each step is a block as high as the risers below it and one run deep; the top one is as deep as the platform. Three 7 in steps with 11 in runs and a 36 in platform, 4 ft wide, take 27.4 cu ft.
Bag yields
What one bag makes, as each maker's data sheet states it, checked October 2026. The bags per cubic yard and per cubic metre leave out waste.
| Bag | Yield | Bags per yd³ | Bags per m³ |
|---|---|---|---|
| 40 lb Quikrete Concrete Mix | 0.3 ft³ · 8.5 L | 90 | 117.7 |
| 50 lb Quikrete Concrete Mix | 0.375 ft³ · 10.6 L | 72 | 94.2 |
| 60 lb Quikrete Concrete Mix | 0.45 ft³ · 12.7 L | 60 | 78.5 |
| 80 lb Quikrete Concrete Mix | 0.6 ft³ · 17 L | 45 | 58.9 |
| 90 lb Quikrete Concrete Mix | 0.675 ft³ · 19.1 L | 40 | 52.3 |
| 50 lb Quikrete Fast-Setting Concrete Mix | 0.375 ft³ · 10.6 L | 72 | 94.2 |
| 40 lb Sakrete High-Strength Concrete Mix | 0.3 ft³ · 8.5 L | 90 | 117.7 |
| 60 lb Sakrete High-Strength Concrete Mix | 0.45 ft³ · 12.7 L | 60 | 78.5 |
| 80 lb Sakrete High-Strength Concrete Mix | 0.6 ft³ · 17 L | 45 | 58.9 |
| 25 kg Sakrete High-Strength Concrete Mix (Canada) | 0.41 ft³ · 11.6 L | 65.9 | 86.1 |
| 30 kg Sakrete High-Strength Concrete Mix (Canada) | 0.5 ft³ · 14.2 L | 54 | 70.6 |
| 20 kg Easy Mix Concrete | 0.353 ft³ · 10 L | 76.5 | 100 |
| 30 kg Easy Mix Concrete | 0.533 ft³ · 15.1 L | 50.6 | 66.2 |
Quikrete, Sakrete and Easy Mix are their owners' trademarks, named only to describe their products; Meadow Tools is not affiliated with any of them.
Tips before you pour
- Check the thickness at several points. A base that dips 1 in under a 4 in slab adds a quarter to the concrete in that area. Level and compact the base first, then measure from a string line.
- Mix one batch size. Quikrete's data sheet asks for about 6 pints of water for each 80 lb bag of Concrete Mix, and a mixer of at least 1 cu ft for each 80 lb bag mixed at once.
- Don't run short mid-pour. A slab poured in two goes leaves a cold joint. Have every bag on site before you start.
Tiling the slab afterwards? The flooring calculator counts the tiles, grout and boxes. For the walls of a new room, the paint calculator works out the gallons or litres, and the room planner lets you draw the space to scale first.