Free concrete calculator — cubic yards, weight and cost
Work out how much concrete you need for a slab, pad, footing or set of post holes. Add as many areas as you need and get cubic yards, bag counts and cost — with the bagged-versus-ready-mix crossover made obvious.
How thick should a slab be?
Four inches is standard for a patio, walkway or shed pad. Five to six inches is what you want for a driveway or anything carrying a vehicle. Six inches with reinforcement is the sensible minimum for a garage floor or anything taking a heavy load.
Order a little over. Sub-grade is never perfectly level, and being half a yard short with a truck on site and concrete going off is a genuinely bad afternoon. Five to ten percent over is normal and cheap insurance.
Know the crossover point. Bagged concrete makes sense up to roughly half a cubic yard — post holes, a small pad, a step. Beyond about one cubic yard, ready-mix is cheaper, vastly faster and more consistent. One cubic yard is 45 bags of 80 pound mix, which is well over a ton of bags to haul, open and mix by hand.
Coverage at a glance
How far one cubic yard goes, and what 1,000 square feet takes, at each common depth:
| Depth | One cubic yard covers | 1,000 sq ft needs |
|---|---|---|
| 4" | 81 sq ft | 12.3 cu yd |
| 5" | 65 sq ft | 15.4 cu yd |
| 6" | 54 sq ft | 18.5 cu yd |
| 8" | 40 sq ft | 24.7 cu yd |
Weight and delivery
Concrete weighs about 2 tons per cubic yard — around 4,000 pounds. This is why ready-mix arrives on a purpose-built truck and why a pickup can carry well under a yard.
Before you order, check access. Bulk material is tipped, not carried — the truck needs room to back in and raise its bed, and most suppliers will not tip on a surface they might damage. Ask about the delivery fee and the minimum order separately, because both change the maths on small jobs.
Turn it into a quote
Hit Copy order and the whole breakdown goes to your clipboard, ready to paste into an estimate. Add your labour, price it with the profit margin calculator, and send it with the estimate generator.
Related: cubic yard calculator, gravel, topsoil, mulch and concrete calculators, plus state-by-state rate data for what landscapers and contractors earn.
FAQ
How much concrete do I need for a 10x10 slab?
A 10 by 10 foot slab at 4 inches thick needs 1.23 cubic yards, which is about 56 bags of 80 pound mix. At that size ready-mix is usually the better call — 56 bags is more than two tons to move and mix.
How many 80 lb bags of concrete make a yard?
Forty-five. An 80 pound bag yields about 0.6 cubic feet, and a cubic yard is 27 cubic feet, so 27 ÷ 0.6 = 45 bags. A 60 pound bag yields 0.45 cubic feet, so it takes 60 of those.
How much does a yard of concrete cost?
Ready-mix pricing varies by region and moves with material costs, so put your local quote into the calculator rather than trusting a national average. Expect a short-load fee on anything under about 3 to 4 yards — that surcharge is often what decides bagged versus delivered.
How much does a yard of concrete weigh?
About 4,000 pounds, or roughly 2 tons. A cubic foot weighs about 150 pounds. This is why you cannot meaningfully haul ready-mix in a standard pickup.
Should I use bagged concrete or ready-mix?
Bagged up to about half a yard, ready-mix beyond one yard, and it is a judgement call in between. Consider the labour honestly: a yard is 45 bags of 80 pound mix, and mixing that by hand while keeping a consistent water ratio across every batch is hard work and hard to do well.
How much concrete do I need for a 30x40 slab?
At 4 inches thick, a 30 by 40 foot slab is 1,200 square feet and needs about 14.8 cubic yards. At 6 inches it is roughly 22.2 cubic yards. Both are firmly ready-mix jobs, and at that size you should order slightly over.