Concrete Calculator
Bags or ready-mix, cubic yards, and waste — counted. Free, instant, and private — everything runs on your device.
4 in typical for a patio
10% covers spillage & uneven subgrade
Your concrete estimate
- Volume (with waste)
- 36.7 cu ft
- Cubic yards (for ready-mix)
- 1.36 cu yd
- Bags — 80-lb
- 62
- Bags — 60-lb
- 82
- Estimated cost (80-lb)
- $372
Over about ½ cubic yard, ready-mix delivery is usually easier and cheaper than mixing bags by hand — the cubic-yard figure is there to compare.
Material estimate only. Footings, foundations, and anything structural must follow your local building code — pull a permit and consult a pro.
Concrete is unforgiving of a short order: once you start a pour you have to finish it, and running back to the store for three more bags means a cold joint in your slab. This calculator gives you the volume in cubic feet and cubic yards, the count in both 60-lb and 80-lb bags, and a waste factor so an uneven subgrade doesn't leave you short. It's built for slabs, pads, walkways, and footings you're placing yourself.
It also shows the cubic-yard figure for a reason: mixing bags by hand is fine for a mailbox post, but past roughly half a cubic yard, ordering ready-mix delivery is both easier and usually cheaper. Anything structural — footings that carry load, foundations — has to follow your local code, so treat this as a material estimate and pull the permit.
How it works
No black box — this is the exact math the calculator runs.
- Volume = length × width × (thickness in inches ÷ 12) × number of slabs, in cubic feet.
- Waste factor (10% default) covers spillage and an uneven subgrade.
- Cubic yards = volume ÷ 27 — how ready-mix is ordered.
- Bags: an 80-lb bag yields ≈ 0.60 cu ft, a 60-lb bag ≈ 0.45 cu ft; counts round up.
- Cost = 80-lb bags × your price per bag.
Last reviewed July 24, 2026 · Fences & Outdoor Structures
Frequently asked questions
How many bags of concrete do I need for a 10x10 slab?
A 10×10 slab at 4 inches thick is about 33 cubic feet. With 10% waste that's roughly 61 eighty-pound bags — which is a lot of mixing. At that size, ready-mix delivery (about 1.4 cubic yards) is the easier and often cheaper call.
How many 80-lb bags make a cubic yard?
An 80-lb bag yields about 0.60 cubic feet, and a cubic yard is 27 cubic feet, so it takes roughly 45 eighty-pound bags to make a yard. Sixty-pound bags yield about 0.45 cu ft, so you'd need about 60 of them.
How thick should a concrete slab be?
4 inches is standard for patios, walkways, and shed floors. Go to 5–6 inches for driveways or anything bearing vehicle weight, and add rebar or wire mesh. Thickness and reinforcement for load-bearing work should follow local code.
When should I use ready-mix instead of bags?
Roughly half a cubic yard is the tipping point. Below it, bagged mix is manageable. Above it, hand-mixing that many bags risks cold joints and inconsistent strength, and delivery is usually cheaper per yard — plus it all goes in at once.