One 80 lb bag of concrete covers 0.6 cubic feet (17-18 sq ft at 4" thickness)

An 80 lb bag of concrete yields 0.6 cubic feet when mixed. At a standard 4-inch thickness, this covers 17-18 square feet. For a 2-inch layer, it extends to 30-36 sq ft. Coverage varies by slab depth, mix type (e.g., quikrete vs. standard), and waste factors like uneven surfaces.

Concrete Coverage Calculator (Per Bag)

Use this formula to estimate:

Square Feet = (Bag Yield in Cubic Feet ÷ Depth in Feet) × 1

80 lb bag: 0.6 cu ft → 18 sq ft at 4", 36 sq ft at 2"
60 lb bag: 0.45 cu ft → 13.5 sq ft at 4", 27 sq ft at 2"
40 lb bag: 0.3 cu ft → 9 sq ft at 4", 18 sq ft at 2"

Factors Affecting Coverage

Slab thickness: Doubling depth (e.g., 4" to 8") halves coverage.
Mix consistency: Wet mixes shrink ~10% when cured; add 5-10% extra material.
Surface texture: Rough or sloped areas require up to 20% more concrete.
Reinforcement: Rebar or wire mesh displaces volume, reducing coverage by 5-15%.

Coverage Comparison by Bag Size & Thickness

Bag Weight	Cubic Feet per Bag	Coverage at 2" Depth	Coverage at 4" Depth	Coverage at 6" Depth
40 lb	0.30	18 sq ft	9 sq ft	6 sq ft
60 lb	0.45	27 sq ft	13.5 sq ft	9 sq ft
80 lb	0.60	36 sq ft	18 sq ft	12 sq ft
90 lb	0.68	40 sq ft	20 sq ft	13.5 sq ft

Pro Tips for Accurate Estimates

Measure volume first: Calculate cubic feet (Length × Width × Depth ÷ 12), then divide by bag yield.
Account for waste: Add 10-15% for spillage, uneven pouring, or formwork gaps.
Use ready-mix for large jobs: Bags exceed $10/cu ft; bulk concrete costs $3-$6/cu ft for 1+ cubic yards.
Check mix specs: High-strength or fiber-reinforced mixes may yield 5-10% less coverage.

Common Mistakes to Avoid

❌ Ignoring depth variations: A 0.5" error in thickness changes coverage by ±12%.
❌ Forgetting subbase: A 4" gravel base reduces concrete volume needed by 25%.
❌ Over-mixing: Adding excess water weakens concrete and increases shrinkage.
❌ Skipping a test pour: Always verify yield with a small batch before full-scale work.