How many bags of concrete for a 4x4 slab? (5x5, 6x6, 8x8 too)
A 4 x 4 ft pad poured 4 inches thick is 5.3 cubic feet of concrete; with 10% waste that is 10 bags of 80 lb, 14 of 60 lb or 16 of 50 lb fast-setting mix, about 800 lb of dry mix in all. A 6 x 6 pad takes 22 bags of 80 lb and an 8 x 8 pad 40, which is about where bags stop being fun. The tables cover 3 x 3 to 8 x 8 ft at 4 and 6 inches, and the metric pads.
Bags for small pads at 4 inches
Bag yields as printed on typical bags: 0.60 cubic feet for 80 lb, 0.45 for 60 lb and 0.375 for 50 lb fast-setting mix, with 10% waste for uneven ground and formwork. The last column is the dry weight of the 80 lb bags, the number to think about before you load the car.
| Pad | Concrete (cu ft) | 80 lb bags | 60 lb bags | 50 lb bags | Dry mix (lb, 80 lb bags) |
|---|---|---|---|---|---|
| 3 x 3 ft | 3 | 6 | 8 | 9 | 480 |
| 4 x 4 ft | 5.3 | 10 | 14 | 16 | 800 |
| 4 x 6 ft | 8 | 15 | 20 | 24 | 1,200 |
| 5 x 5 ft | 8.3 | 16 | 21 | 25 | 1,280 |
| 6 x 6 ft | 12 | 22 | 30 | 36 | 1,760 |
| 6 x 8 ft | 16 | 30 | 40 | 47 | 2,400 |
| 8 x 8 ft | 21.3 | 40 | 53 | 63 | 3,200 |
Six inches for a hot tub or a driveway pad
| Pad | Concrete (cu ft) | 80 lb bags | 60 lb bags | 50 lb bags | Order (cu yd) |
|---|---|---|---|---|---|
| 3 x 3 ft | 4.5 | 9 | 11 | 14 | 0.18 |
| 4 x 4 ft | 8 | 15 | 20 | 24 | 0.33 |
| 4 x 6 ft | 12 | 22 | 30 | 36 | 0.49 |
| 5 x 5 ft | 12.5 | 23 | 31 | 37 | 0.51 |
| 6 x 6 ft | 18 | 33 | 44 | 53 | 0.73 |
| 6 x 8 ft | 24 | 44 | 59 | 71 | 0.98 |
| 8 x 8 ft | 32 | 59 | 79 | 94 | 1.3 |
How the numbers are worked out
Length x width x thickness in feet: 4 x 4 x 0.333 = 5.33 cubic feet. Multiply by 1.10, divide by the bag yield, round up. The concrete calculator does any rectangle or circle, and the bags per cubic yard guide explains the yields. Bigger slabs, where a truck takes over, are in the 10x10 and 12x12 guides.
Mixing that many bags
A wheelbarrow and a hoe handle up to about 6 bags; beyond that rent a mixer, which takes two bags per batch, and have a second person carrying and placing. Pour the pad in one go so it sets as a single piece, and have every bag on site before you start: 22 bags for a 6 x 6 pad is 1,760 lb, two trips in a car or one in a pickup.
Metric: 1.2 to 2.4 m pads
Bags of 25 kg yield about 12 litres of concrete and 20 kg bags about 10 litres, with 10% waste.
| Pad | Thickness | Concrete (L) | 25 kg bags | 20 kg bags |
|---|---|---|---|---|
| 1.2 x 1.2 m | 100 mm | 144 | 14 | 16 |
| 1.5 x 1.5 m | 100 mm | 225 | 21 | 25 |
| 1.8 x 1.8 m | 100 mm | 324 | 30 | 36 |
| 2.4 x 2.4 m | 100 mm | 576 | 53 | 64 |
| 1.2 x 1.2 m | 150 mm | 216 | 20 | 24 |
| 1.5 x 1.5 m | 150 mm | 337 | 31 | 38 |
| 1.8 x 1.8 m | 150 mm | 486 | 45 | 54 |
| 2.4 x 2.4 m | 150 mm | 864 | 80 | 96 |
Before you pour
- Dig out the topsoil, lay and compact 2 to 4 inches of gravel, and set the forms level; a pad that sits on soft ground tips within a year.
- For an AC or heat pump pad, leave the top 1 to 2 inches above grade and check the unit's clearance requirements before you set the size.
- Mesh or fibre in the mix is cheap insurance on anything over 4 x 4; for a hot tub it is required.
- Setting posts instead of a pad? The fence post guide and the sonotube guide cover holes and tubes.
Frequently asked questions
- How many 80 lb bags of concrete for a 4x4 slab?
- 10 bags at 4 inches thick with 10% waste (5.3 cubic feet of concrete), 15 bags at 6 inches. In 60 lb bags: 14 and 20. Any brand of pre-mixed concrete gives the same count for the same bag weight.
- How many bags of concrete for a 4x4 AC pad?
- The same 10 bags of 80 lb at 4 inches; most condenser pads are 3 to 4 inches thick on 2 to 4 inches of compacted gravel, so a 3 x 3 pad at 4 inches is 6 bags. Check the unit's footprint plus 6 inches all round, and keep the pad level with a slight fall away from the house.
- How much concrete for a hot tub pad?
- Hot tubs usually need a 4 inch reinforced pad the size of the tub plus a step: 8 x 8 ft at 4 inches is 40 bags of 80 lb or 0.9 cubic yards from a truck; at 6 inches 59 bags. A filled tub with people in it is several tons, so follow the maker's pad spec and add mesh.
- Should I use bags or ready-mix for an 8x8 slab?
- Either. 40 bags of 80 lb is a morning for two people with a mixer, and 0.9 cubic yards is a small ready-mix order that carries a short-load fee. Price the delivered load; if it is close to the bag total, take the truck and keep your back. The break-even article has the arithmetic.
- How thick should a small concrete pad be?
- 4 inches for an AC unit, a generator, a shed floor or a step landing; 5 to 6 inches with mesh for a hot tub or anything a vehicle drives on. Thinner than 3.5 inches cracks and is not worth the bags saved. Always on a compacted gravel base, never straight on soil.
- How many bags of concrete for a 5x5 or 6x6 slab?
- 5 x 5 at 4 inches: 16 bags of 80 lb or 21 of 60 lb. 6 x 6 at 4 inches: 22 bags of 80 lb, 30 of 60 lb, 36 of 50 lb; at 6 inches 33 bags of 80 lb.
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 2026-09-12. Figures are planning estimates from typical product data: check the yield, size or coverage printed on what you buy and round up.