Concrete calculator: how much concrete do I need?
Tap your project, adjust the size, and the answer updates as you type. You get cubic yards for a ready-mix order and the number of 40, 60 or 80 lb bags for a mix-it-yourself job.
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1 What are you pouring?
2 How big is it?
More options units, extra %, bag size, prices
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How this concrete calculator works
Every shape is turned into cubic feet first. Slabs, patios, driveways and sidewalks are length × width × thickness (inches ÷ 12). Footings and walls are length × width × depth. Post holes are treated as cylinders: π × radius² × depth × number of holes. Steps are figured as solid stairs that sit on the ground, so each step stacks on the one below it.
Then the extra percentage is added, and the total is converted: 27 cubic feet make one cubic yard, and one cubic foot is about 0.0283 cubic meters. Bag counts use the yields Quikrete publishes for its standard Concrete Mix: about 0.30 cu ft per 40 lb bag, 0.45 cu ft per 60 lb bag and 0.60 cu ft per 80 lb bag (Quikrete Concrete Mix data sheet). Other brands and specialty mixes such as fast-setting or high-strength can yield a little differently, so check the back of your bag.
Weight is a rough guide based on normal-weight concrete at about 150 lb per cubic foot (many references use 145–150). It is handy for judging whether a trailer or pickup can carry the bags, not for structural design.
Quick rules of thumb
- One cubic yard ≈ 45 bags of 80 lb mix, 60 bags of 60 lb or 90 bags of 40 lb.
- A 10 × 10 ft slab at 4 inches is about 1.23 cubic yards before extra.
- Post holes are counted as completely full, which leaves a small built-in cushion because the post takes up some room.
- Surfacing over concrete or paving next to it? Our asphalt calculator and gravel base calculator use the same simple approach.
Concrete calculator FAQ
How many bags of concrete are in a cubic yard?
A cubic yard is 27 cubic feet. With Quikrete's published yields that is about 45 bags of 80 lb mix, 60 bags of 60 lb mix or 90 bags of 40 lb mix, before any extra for waste.
How thick should a concrete slab be?
Patios, walks and shed pads are commonly poured about 4 inches thick. Driveways are often 4 to 6 inches, with thicker slabs for heavy trucks or soft soil. Local codes and your contractor have the final say.
How much extra concrete should I order?
Plan on roughly 5 to 10 percent extra for uneven ground, forms that bow out and spillage. Running short halfway through a pour is far worse than having a little left over.
How much does a cubic yard of concrete weigh?
Normal-weight concrete is usually figured at about 145 to 150 lb per cubic foot, so a cubic yard weighs roughly 3,900 to 4,050 lb. Your actual mix can differ.
Should I use bags or order ready-mix?
Bags work well for post holes, small pads and repairs. Once a job reaches about a cubic yard (around 45 bags of 80 lb mix), many people find a ready-mix truck or a rental mixing trailer easier. Ask local suppliers about minimum orders and short-load fees.
Estimate only. Results are planning numbers, not engineering advice or a quote. Measure carefully, confirm the amount, mix and price with your concrete supplier or contractor, and follow local building codes for thickness, base and reinforcement.