How much concrete for a garage floor? (1, 2 and 3 car)
A two-car 24 x 24 ft garage floor poured 4 inches thick is 7.11 cubic yards of concrete; with 10% waste you order 8 yards, one truck. At the 5 inches most garages are poured it is 10 yards, and at 6 inches 11.75. A one-car 12 x 20 ft floor is 3.5 yards at 4 inches (147 bags of 80 lb, which is why nobody uses bags). The tables cover one, two and three car garages at 4, 5 and 6 inches, the thickened edge, and metric floors.
Garage floors at 4 inches
Cubic yards before waste, the order with 10% waste rounded up to the quarter yard, full 10-yard truck loads, and 80 lb bags for comparison. Sizes are the inside of the walls.
| Garage | Floor | Area (sq ft) | Concrete (cu yd) | Order (cu yd) | Trucks | 80 lb bags |
|---|---|---|---|---|---|---|
| 1 car | 12 x 20 ft | 240 | 2.96 | 3.5 | 1 | 147 |
| 1 car, deep | 14 x 24 ft | 336 | 4.15 | 4.75 | 1 | 206 |
| 2 car | 20 x 20 ft | 400 | 4.94 | 5.5 | 1 | 245 |
| 2 car | 24 x 24 ft | 576 | 7.11 | 8 | 1 | 352 |
| 2 car, deep | 24 x 30 ft | 720 | 8.89 | 10 | 1 | 440 |
| 3 car | 32 x 24 ft | 768 | 9.48 | 10.5 | 2 | 470 |
| 3 car, deep | 36 x 24 ft | 864 | 10.67 | 11.75 | 2 | 528 |
Garage floors at 5 inches
| Garage | Floor | Concrete (cu yd) | Order (cu yd) | Trucks | 80 lb bags |
|---|---|---|---|---|---|
| 1 car | 12 x 20 ft | 3.7 | 4.25 | 1 | 184 |
| 1 car, deep | 14 x 24 ft | 5.19 | 5.75 | 1 | 257 |
| 2 car | 20 x 20 ft | 6.17 | 7 | 1 | 306 |
| 2 car | 24 x 24 ft | 8.89 | 10 | 1 | 440 |
| 2 car, deep | 24 x 30 ft | 11.11 | 12.25 | 2 | 550 |
| 3 car | 32 x 24 ft | 11.85 | 13.25 | 2 | 587 |
| 3 car, deep | 36 x 24 ft | 13.33 | 14.75 | 2 | 660 |
Garage floors at 6 inches for lifts and heavy trucks
| Garage | Floor | Concrete (cu yd) | Order (cu yd) | Trucks | 80 lb bags |
|---|---|---|---|---|---|
| 1 car | 12 x 20 ft | 4.44 | 5 | 1 | 220 |
| 1 car, deep | 14 x 24 ft | 6.22 | 7 | 1 | 308 |
| 2 car | 20 x 20 ft | 7.41 | 8.25 | 1 | 367 |
| 2 car | 24 x 24 ft | 10.67 | 11.75 | 2 | 528 |
| 2 car, deep | 24 x 30 ft | 13.33 | 14.75 | 2 | 660 |
| 3 car | 32 x 24 ft | 14.22 | 15.75 | 2 | 704 |
| 3 car, deep | 36 x 24 ft | 16 | 17.75 | 2 | 792 |
The thickened edge
Many garage slabs are monolithic: the outer 12 inches drops to 12 inches deep to carry the walls. That strip is extra concrete on top of the tables above. For a 4 inch slab the extra is the perimeter x 1 ft x 8 inches, with waste:
| Floor | Extra concrete (cu yd) |
|---|---|
| 12 x 20 ft | 1.74 |
| 14 x 24 ft | 2.06 |
| 20 x 20 ft | 2.17 |
| 24 x 24 ft | 2.61 |
| 24 x 30 ft | 2.93 |
| 32 x 24 ft | 3.04 |
| 36 x 24 ft | 3.26 |
Add it to the slab order and round up again. On a 24 x 24 ft two-car floor at 4 inches that takes the order from 8 to about 10.75 yards. If the walls sit on a separate footing, skip this table.
How the numbers are worked out
Width x length x thickness in feet, divided by 27: 24 x 24 x 0.333 / 27 = 7.11 cubic yards. Add 10% for the base that is never perfectly flat, round up to the plant's quarter yard. The concrete calculator does the arithmetic for any size, and the thickened edge is just a second slab entry: perimeter as the length, 1 ft wide, 8 inches thick. The driveway guide covers the apron outside the door, and the shed slab article walks through base, forms and pour for a smaller version of the same job.
Before the truck comes
- 4 inches of compacted gravel, then a 6 mil (or 10 mil) polyethylene vapour barrier directly under the slab; a garage floor without one sweats every spring.
- Wire mesh or fibre on a 4 inch floor; #4 rebar on 18 inch centres on a 6 inch floor. Keep the steel at mid-depth on chairs, not lying on the barrier.
- Control joints in a grid no more than 10 to 12 ft apart, cut the same day; a 24 x 24 ft floor gets one joint each way.
- Slope the floor 1/8 inch per foot to the door and keep the top of the slab at least 4 inches above the driveway outside.
Metric: 3 x 6 to 7 x 8 m garages
Cubic metres before waste, the ready-mix order with 10% waste rounded up to the quarter cubic metre, and 25 kg bags for comparison.
| Floor | Thickness | Concrete (m³) | Order (m³) | 25 kg bags |
|---|---|---|---|---|
| 3 x 6 m | 100 mm | 1.8 | 2 | 165 |
| 3.5 x 7 m | 100 mm | 2.45 | 2.75 | 225 |
| 6 x 6 m | 100 mm | 3.6 | 4 | 330 |
| 6 x 7 m | 100 mm | 4.2 | 4.75 | 385 |
| 7 x 8 m | 100 mm | 5.6 | 6.25 | 514 |
| 3 x 6 m | 150 mm | 2.7 | 3 | 248 |
| 3.5 x 7 m | 150 mm | 3.68 | 4.25 | 337 |
| 6 x 6 m | 150 mm | 5.4 | 6 | 495 |
| 6 x 7 m | 150 mm | 6.3 | 7 | 578 |
| 7 x 8 m | 150 mm | 8.4 | 9.25 | 770 |
Frequently asked questions
- How many yards of concrete for a 24x24 garage?
- 7.11 cubic yards at 4 inches, 8.89 at 5 inches and 10.67 at 6 inches, before waste. Order 8, 10 or 11.75 yards with 10% waste, rounded to the quarter yard. Add about 2.61 yards if the edges are thickened to 12 inches.
- How much concrete for a 20x20 garage slab?
- 4.94 cubic yards at 4 inches before waste, 5.5 yards ordered; at 5 inches 7 and at 6 inches 8.25. One truck in every case.
- How thick should a garage floor be?
- 4 inches is the code minimum for a residential garage in most places, on 4 inches of compacted gravel with a vapour barrier. 5 inches with wire mesh or fibre is the usual spec for a two-car garage; 6 inches with rebar where a lift, a heavy truck or a workshop machine will stand. The thickened edge under the walls is typically 12 inches deep and 12 inches wide.
- How many truck loads for a 3 car garage?
- A 32 x 24 ft three-car floor at 5 inches is 13.25 yards, 2 truck loads at 10 yards a truck; 36 x 24 ft at 6 inches is 17.75 yards, 2 loads. Book the trucks back to back so the next one arrives before the previous pour starts to set, or the floor gets a cold joint.
- Can I pour a garage floor with bags of concrete?
- A 12 x 20 ft one-car floor at 4 inches is 147 bags of 80 lb, 11,760 lb of dry mix, mixed two bags at a time and placed before the first batch sets. It has been done; it is a long day for three people with a mixer, and a 3.5 yard short load is usually cheaper once you add the mixer rental. Two-car floors are truck only.
- Does the garage floor slope?
- Yes, about 1/8 inch per foot towards the door (or a centre drain) so melting snow and wash water run out. On a 24 ft deep garage that is 3 inches of fall from back to front; it does not change the volume enough to matter, as the average thickness stays the same.
More guides
- How many bags of concrete for a 10x10 slab?
Bags of 80, 60 and 40 lb concrete for a 10 x 10 ft slab at 4, 5 and 6 inches with 10% waste, plus the metric 3 x 3 m version in 25 kg and 20 kg bags.
- How many bags of concrete per fence post?
Bags of 80, 60 and 50 lb concrete per 4x4 or 6x6 fence post for 8, 10 and 12 inch holes at 24, 30 and 36 inches deep, plus the metric 100 mm post in 25 kg bags.
- How many bags of concrete in a cubic yard?
80, 60, 50 and 40 lb bags per cubic yard and per cubic foot, 25 kg and 20 kg bags per cubic metre, what a yard of bags weighs, and when a ready-mix truck makes sense.
- How much concrete for a 12x12 slab? (plus 16x16, 20x20, 24x24)
Cubic yards and bags of concrete for 12x12, 16x16, 20x20 and 24x24 ft slabs at 4 and 6 inches with 10% waste, the 4 x 4 m metric slab, and the point where ready-mix wins.
Last updated 2026-09-13. Figures are planning estimates from typical product data: check the yield, size or coverage printed on what you buy and round up.