How Much Concrete Do I Need? A Complete Guide

Calculating Concrete Volume

The formula is straightforward: Length × Width × Depth = Volume. The key is getting your units right and always ordering more than the exact calculation.

Step-by-Step

1. Measure your area in feet for length and width, and inches for depth/thickness.
2. Convert depth to feet by dividing inches by 12. A 4-inch slab = 0.333 feet.
3. Multiply L × W × D (all in feet) to get cubic feet.
4. Divide by 27 to convert to cubic yards (the standard ordering unit).
5. Add 10% for waste, spillage, and uneven ground.

Standard Thicknesses

• Walkways and patios: 4 inches
• Driveways: 6 inches
• Garage floors: 6 inches
• Foundation footings: 8–12 inches

Bags vs. Ready-Mix

For small projects under 1–2 cubic yards, pre-mixed bags are practical. An 80-lb bag yields about 0.6 cubic feet of concrete. For larger projects, ordering a ready-mix truck delivery is more cost-effective and ensures consistent quality.

A typical ready-mix truck holds 8–10 cubic yards. Most companies have a minimum delivery of 1 cubic yard, with short-load fees for small orders.

Quick Reference

• 10×10 ft patio (4"): 1.23 cubic yards ≈ 56 bags (80 lb)
• 20×20 ft driveway (6"): 7.4 cubic yards — order ready-mix
• 4×4 ft post hole (3 ft deep): 0.59 cubic yards ≈ 27 bags

Use our Concrete Calculator for instant calculations with bag counts and waste allowance.