How do I calculate cubic yards of concrete?

Multiply length × width × depth (all in feet), then divide by 27 to get cubic yards. For example, a 10 × 12 ft slab, 4 inches thick: 10 × 12 × 0.333 = 40 cu ft ÷ 27 = 1.48 cubic yards. Add 5-10% for waste.

How many bags of concrete do I need?

A standard 80-lb bag of concrete mix yields about 0.6 cubic feet. For 1 cubic yard (27 cu ft), you need approximately 45 bags of 80-lb mix. For small projects, bags are practical; for anything over 1 cubic yard, ready-mix delivery is usually more cost-effective.

How heavy is concrete?

Standard concrete weighs approximately 150 pounds per cubic foot (2,400 kg per cubic meter). One cubic yard weighs about 4,050 pounds (1,837 kg). Lightweight concrete is about 115 lbs/cu ft.

Concrete Volume: Cubic Yards and Cubic Meters Guide

Concrete Volume Formulas

Rectangular Slab

Cu yd = (Length ft × Width ft × Thickness ft) ÷ 27

Circular Column/Pier

Cu yd = (π × Radius² ft × Height ft) ÷ 27

Slab Volume Quick Reference (4" thick)

Dimensions (ft)	Sq Feet	Cu Yards	80-lb Bags
8 × 10	80	0.99	~45
10 × 10	100	1.23	~56
10 × 12	120	1.48	~67
12 × 12	144	1.78	~81
12 × 20	240	2.96	~135
20 × 20	400	4.94	~225
20 × 24	480	5.93	~270

Volume Unit Conversions

Unit	Cubic Yards	Cubic Feet	Cubic Meters
1 cubic yard	1	27	0.7646
1 cubic foot	0.0370	1	0.0283
1 cubic meter	1.3079	35.315	1

Concrete Weight

Volume	Weight (lbs)	Weight (kg)
1 cubic foot	150	68
1 cubic yard	4,050	1,837
1 cubic meter	5,291	2,400

Ordering Tips

Always add 5-10% extra for waste, spillage, and uneven subgrade
Ready-mix trucks typically deliver 8-10 cubic yards per load
Minimum delivery is often 1 cubic yard; short-load fees apply under this
Order slightly more rather than running short mid-pour

Convert volumes with our volume converter.