How it works
For a slab or rectangular footing, volume = length × width × depth, with each measurement converted to feet. For a post hole or column, volume = π × (diameter ÷ 2)² × depth.
Order volume = pour volume × (1 + waste ÷ 100). Bags = ceil(order volume ÷ the chosen bag yield − 1e-9). Cubic yards = cubic feet ÷ 27. The calculation uses full precision until the final display.
QUIKRETE Concrete Mix yields; other products differ — check your bag. The yields are 0.30 cu ft for 40 lb, 0.375 cu ft for 50 lb, 0.45 cu ft for 60 lb, 0.60 cu ft for 80 lb and 0.675 cu ft for the 90 lb bag, which is sold only in some regions.
Worked example
A 10 × 10 ft slab, 4 in deep, needs 33.33 cu ft (1.23 cu yd) before waste. With 10% waste, the bag basis is 36.67 cu ft.
Using an 80 lb bag yielding 0.6 cu ft: 61.1 → 62 bags. Using a 60 lb bag yielding 0.45 cu ft: 81.5 → 82 bags. Total selected bag weight is 4,960 lb.
Tips and common mistakes
- Depth often uses inches while length and width use feet. Check the selector beside every measurement.
- Waste is an editable planning allowance. It does not account for every uneven surface or over-excavated spot.
- A post-hole estimate treats the hole as a full cylinder and does not subtract a post. Round column uses the same geometry.
- Above about 1 cu yd, compare bag mixing with ready-mix delivery and the supplier's minimum order.
- This is a material estimate. It does not specify structural dimensions, reinforcement or curing requirements.
Questions about this calculator
How many 80 lb bags of concrete are in a yard?
A cubic yard is 27 cubic feet. An 80 lb bag of Quikrete Concrete Mix yields about 0.60 cu ft, so it takes 45 bags per cubic yard before waste.
Other bag sizes:
- 60 lb (0.45 cu ft): 60 bags;
- 50 lb (0.375 cu ft): 72 bags;
- 40 lb (0.30 cu ft): 90 bags;
- 90 lb (0.675 cu ft, sold only in some regions): 40 bags.
Add your waste allowance on top.
How many bags of concrete do I need for a 10x10 slab?
At 4 inches deep, a 10 × 10 ft slab is 33.33 cu ft (1.23 cu yd). That is 56 bags of 80 lb concrete before waste, or 62 bags with 10% waste. With 60 lb bags it is 82 bags with 10% waste.
Change the depth or bag size in the calculator to see your own number.
How much area does a 60 lb bag of concrete cover?
It depends on the depth. A 60 lb bag yields about 0.45 cu ft, which covers about 1.35 sq ft at 4 inches deep. An 80 lb bag (0.60 cu ft) covers about 1.8 sq ft at 4 inches.
How do I work out how many bags of concrete I need?
Multiply length × width × depth in feet to get cubic feet. Add your waste percentage, divide by the bag's yield in cubic feet, and round up to a whole bag. The yield is printed on the bag; for Quikrete Concrete Mix it is 0.30, 0.375, 0.45, 0.60 and 0.675 cu ft for the 40, 50, 60, 80 and 90 lb bags.
Sources
QUIKRETE Concrete Mix yields; other products differ — check your bag.
Values marked with a link come from the linked source, which opens in a new tab. Unit conversions and our own defaults are listed separately. Every value the site uses is in the methodology source register.
Where the numbers come from 8
- 40 lb concrete bag yield
- 0.3 cu ft/bag
- QUIKRETE Concrete Mix No. 1101 data sheet (revised October 2022) (opens in a new tab)quikrete.com · PDF
- 50 lb concrete bag yield
- 0.375 cu ft/bag
- QUIKRETE Concrete Mix No. 1101 data sheet (revised October 2022) (opens in a new tab)quikrete.com · PDF
- 60 lb concrete bag yield
- 0.45 cu ft/bag
- QUIKRETE Concrete Mix No. 1101 data sheet (revised October 2022) (opens in a new tab)quikrete.com · PDF
- 80 lb concrete bag yield
- 0.6 cu ft/bag
- QUIKRETE Concrete Mix No. 1101 data sheet (revised October 2022) (opens in a new tab)quikrete.com · PDF
- 90 lb concrete bag yield
- 0.675 cu ft/bag
- QUIKRETE Concrete Mix No. 1101 data sheet (revised October 2022) (opens in a new tab)quikrete.com · PDF
- Concrete bag sizes offered
- 40, 50, 60, 80, 90 lb
- QUIKRETE Concrete Mix No. 1101 data sheet (revised October 2022) (opens in a new tab)quikrete.com · PDF
- Meters per international foot
- 0.3048 m/ft
- NIST, international foot conversion (opens in a new tab)nist.gov
- Kilograms per pound
- 0.45359237 kg/lb
- NIST Guide to the SI, pound conversion; exact definition (opens in a new tab)nist.gov
Unit conversions and our defaults13
- Inches per foot
- 12 in/ft
- Unit definition: one foot contains twelve inches
- Cubic feet per cubic yard
- 27 cu ft/cu yd
- Geometry: 3 × 3 × 3 feet
- Centimeters per meter
- 100 cm/m
- Metric prefix definition: centi is one hundredth
- Percent denominator
- 100 %
- Definition of percent: parts per hundred
- Circle constant π
- ≈ 3.14159 unitless
- Circle geometry, as specified in the owner brief
- Bag concrete waste default
- 10 %
- Owner planning default; editable
- Volume and weight display precision
- 2 decimal places
- Owner specification: display volume and tons to two decimals
- Count rounding tolerance
- 1e-9 unitless
- Owner specification: ceil(x − 1e-9)
- Bag calculator starting slab dimensions
- 10, 10, 4 ft length, ft width, in depth
- Owner worked example; editable starting measurements, not a recommended pour
- Round-shape starting diameter
- 10 in
- Owner fence-post example; editable starting measurement, not a hole-size recommendation
- Bag calculator starting bag size
- 80 lb
- Owner worked example; editable selection
- Concrete depth unit-check threshold
- 12 in
- Owner specified unit-check warning, not a structural depth limit
- Ready-mix comparison prompt threshold
- 1 cu yd
- Owner planning prompt: compare delivery above about one cubic yard