How much concrete do I need?

The formula

Cubic yards = (L × W × D) / 27

All measurements in feet. If your depth is in inches, divide by 12 first.

Example: 10 × 12 patio, 4 inches thick

• L × W × D = 10 × 12 × (4/12) = 10 × 12 × 0.333 = 40 cubic feet
• 40 / 27 = 1.48 cubic yards
• Order ~1.6 cubic yards to allow for waste

Typical slab depths

• Patios, walkways: 4 inches
• Driveways: 4-6 inches
• Garage floors: 4-6 inches
• Heavy vehicle pads: 6-8 inches
• Footings for houses: 8-12 inches

Bag vs. truck

• A standard 80-lb bag of pre-mix = 0.6 cubic feet = about 1/45 yard
• Small projects (< 1 yard) → bags from a hardware store
• Medium projects (1-3 yards) → mini-mix truck or mix on site
• Large projects (3+ yards) → ready-mix truck delivery; most charge short-load fees under 5 yards

Common mistakes

• Forgetting to convert depth from inches to feet
• Not ordering 5-10% extra for uneven sub-base
• Measuring in irregular shapes without breaking them into rectangles first