Concrete Calculator
Estimate how much concrete you need by area and depth — plus bags and total cost. Switch between imperial and metric units.
Concrete Calculator
Estimate how much you need — and the cost.
- cubic feet 33.33
- cubic meters 0.944
- tons (US) 2.5
- tonnes 2.27
Quick coverage reference
1 cubic yard = 27 cu ft, covering about 81 sq ft at 4 in / 54 sq ft at 6 in; an 80 lb pre-mix bag yields about 0.6 cu ft (about 45 bags per cubic yard).
How it's calculated
- Standard concrete density is about 150 lb/cu ft (= 4050 lb/cu yd); it varies slightly with mix and aggregate.
- Sidewalks / slabs: 4 in; driveways or load-bearing areas: 5–6 in; footings per project spec.
Source: inchcalculator.com/concrete-calculator/ (density 150 lb/cu ft, 80 lb bag = 0.6 cu ft cross-checked)
How much concrete do I need?
Concrete is ordered by the cubic yard for ready-mix, or mixed from bags for small jobs. The volume you need is the area of the slab multiplied by its thickness.
Use cubic yards = area (sq ft) × thickness (in) ÷ 324. One cubic yard fills about 81 sq ft at the typical 4-inch slab thickness. If you're mixing from bags, an 80 lb bag yields about 0.6 cu ft, so it takes roughly 45 bags to make one cubic yard — the calculator shows the bag count so you can decide between bags and ready-mix.
How to measure for concrete
Measure the slab
Length × width in feet. For footings or odd shapes, split into rectangles and total the volume.
Set the thickness
4 inches for patios, walkways, and shed bases; 5–6 inches for driveways and anything bearing vehicle loads.
Read yards and bags
Get cubic yards plus the number of 80 lb bags, so you can compare mixing it yourself against ordering ready-mix.
Add 5–10% extra
Uneven sub-grade and spillage eat into volume. Order a little over so you do not stop a pour halfway.
Concrete thickness & buying tips
Bagged mix suits small jobs up to roughly half a yard. Beyond that, bagging gets expensive and slow — ready-mix delivery is better.
4 inches handles foot traffic and patios; step up to 5–6 inches wherever vehicles will park or drive.
A cold joint forms if a pour is interrupted. Always order a margin over the exact figure so the slab goes in continuously.
Concrete calculator FAQ
How many 80 lb bags of concrete are in a cubic yard?
About 45 bags, since each 80 lb bag yields roughly 0.6 cubic feet and a cubic yard is 27 cubic feet. (60 lb bags ≈ 60 per yard.)
How much does a yard of concrete cover?
One cubic yard covers about 81 sq ft at 4 inches thick, 65 sq ft at 5 inches, or 54 sq ft at 6 inches.
How thick should a concrete slab be?
4 inches is standard for patios and walkways; use 5–6 inches for driveways or anything carrying vehicle weight.
When should I order ready-mix instead of bags?
Once you need more than about half a cubic yard. Beyond that, bags become costly and hard to mix fast enough.
How much does a cubic yard of concrete weigh?
About 4,050 lb (roughly 2 tons), based on standard concrete density of 150 lb per cubic foot.