How thick should a concrete slab be?

Patios and walkways: 4 in is common. Driveways and garage slabs: 4–6 in depending on load. Enter your thickness and the calculator handles volume and bags.

How much concrete for a 10×10 slab?

A 10×10 ft × 4 in slab is about 1.23 yd³ before waste. With 10% waste, order roughly 1.36 yd³ or use the bag count shown in the calculator.

How many 80 lb concrete bags do I need?

Divide your volume in cubic feet by the bag yield (80 lb ≈ 0.60 ft³ per bag), add your waste factor, then round up. Our calculator does this live, e.g. a 12×10×4 in slab with 10% waste needs 74 bags.

Should I buy bags or ready-mix?

Small jobs under ~1 yd³ are usually cheaper and easier with bags. Larger slabs and driveways are ordered by the cubic yard from a ready-mix supplier. We show both bag count and order-ready yards.

Concrete Slab Calculator

Use this slab preset for flat pours, patios, sidewalks, and garage floors. Enter length, width, and thickness in inches; we include 10% waste so you do not run short at the store.

No signup
Formula shown
Free forever

Dimensions

Shape

Units

Length (ft)

Width (ft)

Thickness (in)

Spillage & Waste (10%)Includes extra so you don't run short

Bag size

Using a pump truck?

Adds 0.5 yd³ to fill the priming lines

Price per bag ($, optional)

Price per yd³ ($, optional)

Result

74 bags (80 lb)

1.6296 yd³ with 10% waste · order 1.75 yd³ ready-mix

How we calculated it

12 ft × 10 ft × 4 in ÷ 12 = 40.00 ft³
+10% waste = 44.00 ft³
44.00 ft³ ÷ 27 = 1.6296 yd³

Yield based on Quikrete/Sakrete published data: 0.60 ft³ per 80 lb bag. Formula: L × W × (T/12) ÷ 27 = yd³. Full methodology

Plan the rest of your project

Embed this calculator on your site

Copy the iframe code below. Free to use. Include the attribution link shown in the embed.

<iframe src="https://www.qtycalc.com/embed/concrete" width="100%" height="780" style="border:1px solid #e5e7eb;border-radius:8px;" title="Concrete Calculator" loading="lazy"></iframe>

Use this slab preset for flat pours, patios, sidewalks, and garage floors. Enter length, width, and thickness in inches; we include 10% waste so you do not run short at the store.

Bill this job

Bill this job — free PDF template

How to write a contractor invoice →

Frequently asked questions

How thick should a concrete slab be?: Patios and walkways: 4 in is common. Driveways and garage slabs: 4–6 in depending on load. Enter your thickness and the calculator handles volume and bags.
How much concrete for a 10×10 slab?: A 10×10 ft × 4 in slab is about 1.23 yd³ before waste. With 10% waste, order roughly 1.36 yd³ or use the bag count shown in the calculator.
How many 80 lb concrete bags do I need?: Divide your volume in cubic feet by the bag yield (80 lb ≈ 0.60 ft³ per bag), add your waste factor, then round up. Our calculator does this live, e.g. a 12×10×4 in slab with 10% waste needs 74 bags.
Should I buy bags or ready-mix?: Small jobs under ~1 yd³ are usually cheaper and easier with bags. Larger slabs and driveways are ordered by the cubic yard from a ready-mix supplier. We show both bag count and order-ready yards.

Bill this job

Frequently asked questions

Related calculators & guides