Concrete Slab Calculator: Slab, Pad & Driveway Yardage

Use this concrete slab calculator to estimate how much concrete you need for flatwork projects like slabs, pads, patios, floors, and driveways. Enter length, width, and thickness to get results in cubic yards (for ordering ready-mix), cubic feet, and optional estimates for bags of concrete and concrete weight. If you need a quick concrete measurement calculator for rectangular areas, this page keeps it simple and accurate.

Cubic feet: ft³ = Length(ft) × Width(ft) × Thickness(ft)

Thickness conversion: Thickness(ft) = inches ÷ 12

Cubic yards: yd³ = ft³ ÷ 27

This rectangular-area math is the core of any concrete calculator slab estimate for flatwork.

Use the same slab formula for a concrete pad calculator estimate. Pads for sheds, equipment, or small landings are typically simple rectangles. Measure carefully and confirm thickness—small changes in thickness can noticeably change yardage.

This page also works as a concrete driveway calculator for straight rectangular driveways. If your driveway flares or has multiple sections, break it into rectangles and add the volumes together. Consider ordering extra (5–10%) for waste, spillage, and subgrade variation.

For interior flatwork, this concrete floor calculator approach is the same: length × width × thickness. If your floor includes thickened edges, trenches, or multiple depths, calculate each section separately and sum them for a more accurate total.

Example: 20 ft × 10 ft slab at 4 inches thick.

• Thickness(ft) = 4 ÷ 12 = 0.3333 ft
• Volume(ft³) = 20 × 10 × 0.3333 ≈ 66.67 ft³
• Volume(yd³) = 66.67 ÷ 27 ≈ 2.47 yd³

With 5% waste: 2.47 × 1.05 ≈ 2.59 yd³.

If you’re not ordering ready-mix, estimate bag counts using volume in cubic feet and bag yield. Typical planning yields are:

• 60 lb bag: ~0.45 ft³
• 80 lb bag: ~0.60 ft³

Bag formula: Bags = Total ft³ ÷ Bag Yield

For the best accuracy, always use the yield printed on your bag (brands and mixes vary).

Concrete is heavy. A common planning estimate is ~150 lb per cubic foot.

• Weight (lb) = ft³ × 150
• Weight (lb) = yd³ × 4,050

This helps with hauling, staging, access, and DIY mixing logistics.

• Verify thickness: Don’t guess—measure forms or specs.
• Break complex shapes: Split into rectangles and sum volumes.
• Use a waste factor: 5% is common; 10% is safer for uneven subgrade or first-time pours.
• Order by yards: Ready-mix suppliers typically sell by cubic yard (yd³).

This tool also works as a concrete patio calculator. Patios are typically slab-style pours—measure length, width, and thickness, then add a 5–10% waste factor for spillage and grade variation. If your patio has multiple sections or curves, split it into rectangles, calculate each section, and add the totals.

If you searched for a concrete calculator slab, use the calculator above to enter length, width, and thickness to estimate cubic yards and bags for your project.