Concrete Calculator
Pouring a patio slab, a shed base or a run of fence-post footings? This concrete calculator converts your dimensions into cubic yards of concrete, the number of bags you would need to mix, and the weight involved — so you can decide between bagged mix and a ready-mix truck before the first shovel hits the ground.
Enter the length, width and thickness below. The concrete calculator works in yards, cubic feet, tons, bags and cost side by side, using the standard weight of about 4,050 lb per cubic yard. For flatwork, treat it as a concrete slab calculator with the bag count and weight built in.
Cubic Yard Calculator
Length × Width × Depth → cubic yards, tons, bags & cost. Free, no sign-up.
Most mulch and topsoil beds need 2–3 inches; gravel driveways 4–6 inches.
The material sets the weight and bag estimate — densities are typical averages.
Add your supplier’s price to see the estimated total cost.
Suggested order: 1.50 cubic yards (exact need 0.93 yd³ + 10% for waste & compaction).
(2,130 lb)
using 1.5 cu ft bags
add a price per yard to see the cost
Order tip: add 5–10% extra for waste, spillage and compaction — material settles once it is spread and rained on. The suggested order amount above already includes a 10% allowance, rounded up to the nearest half yard.
How to Calculate Concrete in Cubic Yards
The concrete calculator above runs this formula for you — like any concrete volume calculator, it starts from length × width × thickness. Here it is in full, because concrete is the one material where running short mid-pour is a real problem:
Cubic yards = (length in feet × width in feet × thickness in feet) ÷ 27
Thickness is usually given in inches, so divide it by 12 first. Worked example — a 10 ft × 10 ft patio slab, 4 inches thick (the standard slab thickness):
- Convert the thickness: 4 in ÷ 12 = 0.33 ft
- Multiply the volume: 10 ft × 10 ft × 0.33 ft = 33.3 cubic feet
- Convert to yards: 33.3 ÷ 27 = 1.23 cubic yards
- In 60 lb bags: 33.3 ÷ 0.45 cu ft yield per bag = 75 bags
- Weight: 1.23 yd³ × 4,050 lb = about 5,000 lb, or 2.5 tons
With the 10% allowance for spillage, uneven subgrade and forms that are not perfectly level, the suggested order is 1.5 cubic yards — a far better outcome than a cold joint because the truck or the bag pile ran out. That yards number — the concrete calculator’s yards figure — is the one you quote to the ready-mix dispatcher.
How Many Bags of Concrete per Cubic Yard?
This is the concrete calculator bags view — bagged concrete is sold by yield: a 60 lb bag makes about 0.45 cubic feet of concrete, and an 80 lb bag makes about 0.6 cubic feet. That gives these bag counts:
| Cubic yards | 60 lb bags | 80 lb bags |
|---|---|---|
| 1 | 60 | 45 |
| 2 | 120 | 90 |
| 3 | 180 | 135 |
| 5 | 300 | 225 |
| 10 | 600 | 450 |
As a rule of thumb, bags are convenient below about half a cubic yard — a few footings, a small pad, a repair. Around one cubic yard (60 bags, mixed one or two at a time) most people find ready-mix wins on time and consistency, even after short-load fees. A dedicated concrete bag calculator would stop at the count; here the yards figure also tells you when to stop bagging and order the truck.
How Much Does a Cubic Yard of Concrete Weigh?
A cubic yard of concrete weighs about 4,050 lb — just over 2 tons. That is why a standard ready-mix truck carries 8–10 yards at most, and why the 10 × 10 slab in the example above puts roughly 2.5 tons of finished weight onto its base.
It is also why the base matters: 4 inches of compacted gravel under the slab spreads that load and keeps the slab from settling and cracking at the corners.
Slab Thickness and Coverage Guide
Four inches is the standard thickness for patios, walkways and shed floors — anything carrying only foot traffic. Driveways and anywhere vehicles park should be 5–6 inches, ideally over a compacted gravel base with reinforcement. Footings are a different shape of pour: they go below the frost line required by your local code, so check the depth before you dig.
Coverage is the quick cross-check: one cubic yard at 4 inches thick covers about 81 square feet, and at 6 inches about 54 square feet. If your supplier’s quote implies very different coverage, one of you has the thickness wrong.
Frequently Asked Questions
How many 80 lb bags of concrete are in a cubic yard?
45 bags. Each 80 lb bag yields about 0.6 cubic feet, and 27 ÷ 0.6 = 45. The 60 lb equivalent is 60 bags per cubic yard.
How many bags do I need for a 10×10 slab?
At the standard 4 inches thick, a 10 × 10 slab is 1.23 cubic yards — that is 75 bags of 60 lb mix, or 56 bags of 80 lb mix. Add roughly 10% extra for waste and an uneven base.
Is it cheaper to use bags or ready-mix?
For small jobs under about half a yard, bags are cheaper once ready-mix short-load fees are counted. For a yard or more, ready-mix is usually cheaper per yard and dramatically faster — compare both using the cost field in the calculator. Enter both prices above and the tool doubles as a concrete slab cost calculator for your exact slab size.
How thick should a concrete driveway be?
5–6 inches, over 4–6 inches of compacted gravel base, with rebar or mesh reinforcement. A 4 inch driveway slab is the most common cause of early cracking under vehicle loads.
More calculators
Pouring in stages? Work out the base first with the gravel calculator, check mixes and bedding with the sand calculator, or use our main calculator for any other material on the project.