How the concrete calculator works
This calculator finds the volume of your pour and converts it into the concrete you need to buy:
- Calculate the volume. Slabs and footings use length ร width ร thickness; walls use length ร height ร thickness; columns use the cylinder formula ฯ ร rยฒ ร height.
- Add waste. We add your waste percentage to cover uneven ground and spilled mix.
- Convert to bags or yards. 27 cubic feet = 1 cubic yard. A 60lb bag yields about 0.45 cu ft; an 80lb bag yields about 0.60 cu ft. We round bag counts up.
Tip: a small 4" slab for a shed or patio is a classic first DIY pour. Anything much larger than a cubic yard is usually cheaper and easier to order as ready-mix.
Worked example: a 10 ร 10 ft patio slab
A small patio is the most common first concrete pour, and it shows the whole method clearly. The slab is 10 ft by 10 ft, poured 4 inches thick, with a 10% waste allowance.
- Find the area. 10 ร 10 = 100 sq ft.
- Convert the thickness to feet. 4 in รท 12 = 0.333 ft.
- Calculate the volume. 100 ร 0.333 = 33.3 cubic feet.
- Add waste. 33.3 ร 1.10 = 36.6 cu ft to order.
- Convert to cubic yards. 36.6 รท 27 = 1.36 cu yd, so you would order 1.5 yards.
- Or in bags. Using 60 lb bags at 0.45 cu ft each: 36.6 รท 0.45 = 81.3, which rounds up to 82 bags. With 80 lb bags at 0.60 cu ft: 36.6 รท 0.60 = 61 bags.
This is the point at which the bags-versus-ready-mix decision gets real. Hauling and mixing 82 bags by hand is a long day for two people, and the mixed concrete arrives in batches that can start to set before you finish. Ordering 1.5 cubic yards delivered is usually both cheaper and better quality once you pass about a cubic yard โ roughly the 60-bag mark.
The same slab at 6 inches thick
A patio only needs 4 inches, but a driveway or anything supporting vehicle weight needs 6. At 6 in the thickness is 0.5 ft, so the volume is 100 ร 0.5 = 50 cu ft, and with 10% waste that is 55 cu ft or 2.04 cubic yards. In 60 lb bags that is 122 bags โ clearly a job for ready-mix delivery.
Pouring several identical shapes
If you are setting eight pier footings of the same size, enter the dimensions once and set Quantity to 8 rather than working out eight separate pours. The calculator multiplies the volume before converting to bags, which is the same as adding them up, and it keeps the waste allowance consistent across the whole order.
Concrete bag yield reference
| Bag size | Approx. yield | Bags per cubic yard |
|---|---|---|
| 40 lb | 0.30 cu ft | 90 |
| 50 lb | 0.38 cu ft | 71 |
| 60 lb | 0.45 cu ft | 60 |
| 80 lb | 0.60 cu ft | 45 |
How much does a cubic yard cover?
| Slab thickness | Coverage per cubic yard |
|---|---|
| 4 in | 81 sq ft |
| 5 in | 64.8 sq ft |
| 6 in | 54 sq ft |
| 8 in | 40.5 sq ft |
What concrete costs in 2026
Concrete is one of the few building materials where the delivery method matters more than the product. Bagged concrete costs far more per cubic yard but has no minimum order; ready-mix is cheap per yard but carries delivery and short-load fees.
| Supply method | Typical 2026 price | Works out to |
|---|---|---|
| 60 lb bag (0.45 cu ft) | $4.50 โ $7.00 per bag | โ $270 โ $420 per cubic yard |
| 80 lb bag (0.60 cu ft) | $6.00 โ $9.00 per bag | โ $270 โ $405 per cubic yard |
| Ready-mix delivered | $140 โ $200 per cubic yard | Plus delivery and short-load fees |
| Short-load surcharge | $50 โ $150 per load | Applies below a full truck (about 10 yards) |
Note what the table says about bags: even at the cheapest end, bagged concrete works out to roughly double the cost per cubic yard of ready-mix. You are paying for convenience and for not having to hit a delivery window.
Running the numbers on the patio example: 82 bags of 60 lb mix at around $5.50 each is roughly $450, before you count the mixer rental. The same 1.5 cubic yards delivered is about $250โ$380 including a short-load fee. For any pour over about a cubic yard, ready-mix wins on both price and consistency.
Hiring the whole job out is a bigger step up. A professionally poured and finished slab in the US typically runs $8 to $18 per square foot including materials, labour, and finishing โ so the 100 sq ft patio lands somewhere between $800 and $1,800. The spread is wide because the base preparation dominates the cost: excavation, a compacted gravel base, forms, and reinforcement can easily exceed the price of the concrete itself.
What moves the number most: your region and local aggregate costs, site access (a truck that cannot reach the pour means a pump, which adds $150โ$400), reinforcement (rebar or wire mesh), and the finish โ a plain float finish is cheapest, while stamped or coloured concrete can double the price.
These are planning figures, not quotes. Ready-mix pricing is quoted locally and varies seasonally, and most plants will price a specific job for free. Use the calculator to get the volume right first, then ask for quotes against that number.
Pro tips
- Buy bags in the same batch. Pre-mixed bag colors can vary slightly between batches.
- Order ready-mix with a margin. Ask the plant for about 1/2 yard over โ running short mid-pour is the worst outcome.
- Add rebar or wire mesh for anything load-bearing, and rent a power mixer if you're doing more than a few bags.
- Wet the subgrade before pouring so dry ground doesn't suck water out of the concrete.