How much concrete do I need for a slab?

Multiply length × width × thickness (all in feet), then divide by 27 to get cubic yards. PourYards also converts volume into 80-lb, 60-lb, and 40-lb bags and suggests bags vs a ready-mix truck. Add about 10% extra for waste on most DIY pours.

How does a concrete slab calculator work?

A concrete slab calculator converts slab dimensions into volume. Thickness in inches is divided by 12 to get feet. Volume in cubic feet is divided by 27 for cubic yards. Bag counts use typical yields such as 0.60 cubic feet per 80-lb bag.

How do I use a concrete pad calculator?

Measure the pad length and width, choose thickness (often 4 inches for light pads), tap a preset like Shed pad 8×8×4 in, and read cubic yards plus bag counts. Turn on the 10% waste option if you want a buffer.

Is a cement calculator the same as a concrete calculator?

People often search cement calculator when they mean bagged concrete mix. Cement is the binder; concrete is cement plus aggregate. PourYards estimates ready-to-use bagged concrete mix by volume, not pure cement powder bags.

How many bags of concrete for a slab?

Divide cubic feet by the bag yield, then round up. Typical yields: 80-lb ≈ 0.60 cu ft, 60-lb ≈ 0.45 cu ft, 40-lb ≈ 0.30 cu ft. Example: a 10×12 ft patio at 4 in is about 1.63 cu yd with 10% waste — roughly 74 bags of 80-lb mix.

How much concrete do I need?

You need about

— yd³

— ft³ · — m³

Buy

— bags

80-lb mix

Also: — × 60-lb · — × 40-lb

Job preset

Shape

Units

Length

Width

Thickness

Add 10% waste Default ON — uneven base & spillage

Show calculation steps

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How the numbers work

Rectangle / trench: cu yd = (L × W × T in feet) ÷ 27
Circle: cu yd = (π × (diameter/2)² × thickness in feet) ÷ 27
Bags: ceil(cu ft ÷ yield). Yields: 80-lb = 0.60, 60-lb = 0.45, 40-lb = 0.30 cu ft

Check the bag label — brands vary. PourYards is independent and not affiliated with QUIKRETE or any manufacturer.

Quick examples

Patio 10×12 at 4 in

40 ft³ → 1.481 yd³ · with 10% → 1.630 yd³

74 bags of 80-lb mix. Borderline: bags or a small truck both work.

Shed pad 8×8 at 4 in

≈21.33 ft³ → 0.790 yd³ · with 10% → 0.869 yd³

40 bags of 80-lb mix. Bag run is usually easier than calling a truck.

FAQ — slab, pad & cement

How much concrete do I need?

Measure the pour, pick a shape, and read the answer at the top. This concrete calculator returns cubic yards plus bag counts and bags-vs-truck advice.

What does a concrete slab calculator include?

A concrete slab calculator turns slab dimensions into order volume. PourYards also shows bag counts, optional 10% waste, and whether bags or ready-mix make more sense.

How do I size a concrete pad?

Use the concrete pad calculator the same way as a slab, or tap Shed pad 8×8×4 in. Light pads are often 4 inches; heavier loads may need thicker pours — follow local code.

Cement calculator vs concrete calculator?

Searchers often type cement calculator when they mean bagged concrete. Cement is only the binder; this tool estimates concrete mix volume and bags.

Bags or a ready-mix truck?

Rule of thumb on this site: under about 1 yd³ → bags; 1–3 yd³ → either works; over about 3 yd³ → call a truck. Labor and mixing time matter as much as price.

Should I add waste?

Yes for most DIY jobs. Add 10% waste is on by default. Toggle it off only if you already padded the dimensions yourself.