Concrete Calculator
Calculate exact cubic yards, cubic feet, and 80 lb, 60 lb, or 40 lb bag counts for concrete slabs, footings, and steps.
- 62 × 80 lb bags of concrete mix
- 1.36 cubic yards total volume (36.67 cu ft / 1.04 m³)
- Note: Ordering ready-mix is usually cheaper above 1 yd³.
Standard Project Worked Example (No JavaScript Required)
Baseline Scenario: 10×10 ft slab, 4 in thick (0% waste): 33.33 ft³, 1.23 yd³, 56 × 80 lb bags, 75 × 60 lb bags. With 10% waste: 1.36 yd³, 62 × 80 lb bags.
Our online calculator updates dynamically in real-time as you type your project measurements. If JavaScript is disabled, use the formula reference below.
How This is Calculated
Slab Volume (cu ft) = Length (ft) × Width (ft) × (Thickness (in) / 12). Cubic Yards = Volume (cu ft) / 27. Bag counts are calculated based on manufacturer nominal yields (80 lb = 0.60 ft³, 60 lb = 0.45 ft³, 40 lb = 0.30 ft³) and rounded UP to the nearest whole bag.
Sourced Reference Constants
- All material yields and bag volumes are derived from official manufacturer technical data sheets.
- Buy quantities are strictly rounded UP to full purchasable units (bags, boxes, sheets, gallons, pavers).
- Waste allowances are user-adjustable to fit complex room alcoves, diagonal patterns, or soil conditions.
Frequently Asked Questions
How many bags of concrete per yard?
One cubic yard of concrete requires 45 bags of 60 lb mix or 34 bags of 80 lb mix (33.75 rounded up). One cubic yard equals 27 cubic feet.
How many bags of concrete per fence post?
A standard 4x4 post set in a 12-inch diameter hole 24 inches deep requires 3 bags of 80 lb mix (or 4 bags of 60 lb mix).
When should I order ready-mix concrete instead of bags?
Ordering ready-mix concrete by truck is usually cheaper and significantly easier for projects exceeding 1 cubic yard (approximately 45 to 56 bags).