Concrete Calculator — Cubic Yards, Bags & Cost

Slab, round footing or steps in — cubic feet, cubic yards and bag counts out.

Quick answer: Calculate cubic yards, 80/60/40 lb bag counts and bag-versus-delivered cost for slabs, round footings and steps, with a 10% waste margin included.

Shape

Length (ft) Width (ft) Thickness (in)

Add 10% waste (recommended) $ per 80-lb bag (optional) $ per 60-lb bag (optional) $ per cubic yard delivered (optional)

📏 Measure twice: thickness drives everything — going from 4 in to 5 in adds 25% volume. Probe the form at its deepest point, including any dip in the subgrade.

How to use

Pick your shape: slab, round footing or steps, and enter the dimensions.
Keep the 10% waste toggle on unless the form is dead-level and generous.
Read cubic yards, then bag counts for whichever bag size you can actually haul.
Optional: enter bag prices or delivered price per yard to compare both routes.

About this tool

Order too little concrete and the pour turns into a cold joint; order too much and it is money in a dumpster. This calculator handles the three pours people actually attempt: rectangular slabs, round footings and simple steps, converting your dimensions into cubic feet, cubic yards and cubic meters, then into 80, 60 and 40 lb bag counts using real yield figures. A 10% waste toggle covers the spillage and uneven subgrade every real pour has, and optional cost fields let you compare buying bags against having a ready-mix truck show up. Curing matters as much as ordering — keep the slab damp for five to seven days and keep vehicles off it for a week. All of the math runs in your browser.

FAQ

How much concrete do I need for a 4-inch slab?

One cubic yard covers 81 sq ft at 4 inches — so divide your square footage by 81. A 10 × 12 patio at 4 in is 120 sq ft ÷ 81 = 1.48 yd³, call it 1.6 yd³ with the 10% waste margin this calculator adds for you.

How much does concrete cost?

Bagged concrete runs about $6–$8 per 80-lb bag, which works out to roughly $135–$180 per cubic yard of yield. Delivered ready-mix is typically $150–$220 per yd³, and most suppliers charge a short-load fee below about 5–10 yd³. Regional prices swing hard — price both routes locally.

How many 80-lb bags make a cubic yard?

An 80-lb bag yields about 0.60 cu ft, and a yard is 27 cu ft, so plan on 45 bags per yard (46 with waste). That is 3,600 lb of hauling — it is why a truck delivery usually wins past half a yard.

How long does concrete take to cure?

It stays workable for 1–2 hours, takes foot traffic in 24–48 hours, vehicle traffic in about 7 days, and reaches full design strength at 28 days. Keep it damp for the first 5–7 days — dry curing is what causes weak, dusty surfaces.

Do I need rebar or wire mesh?

For a 4-inch slab, wire mesh or rebar is cheap insurance against crack propagation; footings and load-bearing slabs genuinely need steel and may need a permit. This tool computes volume only — check your local code for reinforcement requirements.

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Concrete Calculator — Cubic Yards, Bags & Cost

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About this tool

FAQ

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