How to Estimate a Concrete Slab or Driveway: Cubic Yards and Cost

Concrete is ordered by the cubic yard, so every slab estimate starts with converting length, width and thickness into yards — then adding enough extra that you don't run short mid-pour.

Step 1: Calculate cubic yards

Length (ft) × width (ft) × thickness (ft) ÷ 27. Remember thickness is in feet: 4 inches = 0.333 ft.

For a 20 × 30 ft driveway at 4 inches: 20 × 30 × 0.333 = 200 cu ft ÷ 27 = 7.41 cubic yards.

Step 2: Add waste

Uneven subgrade, spillage and form flex eat concrete. Add 5–10%. 7.41 × 1.08 = 8.0, so order 8 yards.

Step 3: Price base, steel and forms

Include compacted gravel base, reinforcement (wire mesh or rebar), and forms. Price reinforcement by area: 600 sq ft × $0.60 = $360.

Step 4: Price it

The rates below are example numbers to show the math. Use your own supplier prices, labor costs and local permit fees.

Line item	Quantity	Rate	Amount
Excavation & haul-off	Allowance	—	$600
Gravel base	10 tons	$35/ton	$350
Ready-mix concrete	8 yd	$165/yd	$1,320
Reinforcement	600 sq ft	$0.60/sq ft	$360
Forms	Allowance	—	$250
Labor (place, finish, saw-cut joints)	30 hrs	$50/hr	$1,500
Subtotal			$4,380
Overhead & profit (25% markup)			$1,095
Total			$5,475

If the truck can't reach the pour, add a pump or buggy line. Ask your supplier about short-load fees on small pours and extra charges for hot-weather or cold-weather additives.

Step 5: Set expectations in writing

• Concrete cracks — explain that control joints are there to guide where.
• State how long before foot traffic and vehicles (follow your mix supplier's guidance).
• Say what happens if you hit rock, roots or soft soil during excavation.

Send it before you leave

Once your numbers are set, the fastest way to win the job is to get the proposal in front of the customer while they're still thinking about it. With Quote Commander you can build the line items on site, text or email the proposal, and let the customer sign and pay a deposit from their phone. See how it works for concrete contractors, or read how to set your markup.

Frequently asked questions

How do I calculate cubic yards of concrete?

Multiply length × width × thickness, all in feet, then divide by 27. A 20 × 30 ft slab at 4 inches is about 7.41 cubic yards.

How much extra concrete should I order?

Most contractors add 5–10% for waste and uneven subgrade.

How thick should a concrete driveway be?

4 inches is common for passenger cars; heavier vehicles often call for 5–6 inches. Follow local code and your engineer or supplier's recommendation.