Concrete calculator: cubic yards and bags
A 10 x 10 ft slab 4 in thick holds 33.3 cubic feet, 1.23 cubic yards, or 1.36 with 10% extra. That is 62 bags of 80 lb premix at about 0.60 cu ft each, or 45 bags per cubic yard before waste. Quikrete rates its 60 lb bag at 0.45 cu ft and its 40 lb bag at 0.30.
Updated · By the Interior Redesign AI editorial team · Sources cited on the page
Bags of premix
62 × 80 lb
1.36 cu yd including 10% waste.
Volume
1.36 cu yd
36.7 cu ft
Yield per bag
0.6 cu ft
Quikrete Concrete Mix data sheet
| 40 lb bags (0.3 cu ft each) | 123 |
|---|---|
| 50 lb bags (0.375 cu ft each) | 98 |
| 60 lb bags (0.45 cu ft each) | 82 |
| 80 lb bags (0.6 cu ft each) | 62 |
Bag yields are for Quikrete Concrete Mix; other brands and fast-setting mixes publish their own. For larger pours, compare the bag count with a ready-mix delivery quote.
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Key numbers
- 80 lb bag
- About 0.60 cu ft (17 L) of concrete (Quikrete Concrete Mix)
- 60 lb bag
- About 0.45 cu ft (12.7 L)
- 50 lb bag
- About 0.375 cu ft (10.6 L)
- 40 lb bag
- About 0.30 cu ft (8.5 L)
- One cubic yard
- 27 cu ft: 45 × 80 lb or 60 × 60 lb bags before waste
- Strength
- 4,000 psi at 28 days (Quikrete Concrete Mix data sheet)
Worked example
A 10 x 10 ft patio slab, 4 in thick
One slab, 80 lb bags of Quikrete Concrete Mix, 10% waste.
- Volume: 10 × 10 × 4 ÷ 12 = 33.3 cu ft.
- With 10% waste: 36.7 cu ft, which is 1.36 cu yd.
- Bags: 36.67 ÷ 0.60 = 61.1, rounded up to 62.
Buy 62 bags of 80 lb concrete mix, or order about 1.36 cubic yards of ready-mix.
How we calculate
Volume is plain geometry: length × width × thickness for a slab or a strip footing, and π × radius² × height for a round column or post hole. Inches are divided by 12 to get feet, and cubic feet by 27 to get cubic yards.
Bags: the volume plus the waste allowance, divided by the yield printed on the Quikrete Concrete Mix data sheet for your bag size, rounded up. Other brands and fast-setting mixes publish their own yields, so check the bag you buy.
Assumption, labeled: we add 10% for an uneven subgrade, spillage and forms that bow. You can set your own allowance; a carefully graded, formed slab may need less.
Estimates, sources
Planning estimates and published guidelines, not quotes, designs or code rulings. Figures were checked on each source on the date shown. Local prices, your home and your jurisdiction's adopted code decide the real answer.
- QUIKRETE Concrete Mix (No. 1101) data sheet (Quikrete, as of Oct 26, 2026): yield per bag approximately 0.30 cu ft (40 lb), 0.375 (50 lb), 0.45 (60 lb), 0.60 (80 lb), 0.675 (90 lb); 4,000 psi at 28 days (sheet revised October 2022)
- Setting Posts: project instructions (Quikrete, as of Oct 26, 2026): hole diameter three times the width of the post; depth 1/3 to 1/2 of the post's above-ground length, plus 6 in; 6 in of gravel in the bottom; fill concrete to 3-4 in below ground level (undated page)
Bags of concrete per cubic yard
Rounded up, before any waste allowance, from the yields on the Quikrete Concrete Mix data sheet.
| Bag size | Yield per bag | Bags per cubic yard |
|---|---|---|
| 40 lb | 0.3 cu ft | 90 |
| 50 lb | 0.375 cu ft | 72 |
| 60 lb | 0.45 cu ft | 60 |
| 80 lb | 0.6 cu ft | 45 |
Post holes and round footings
A 12 in hole 36 in deep holds 2.36 cu ft, 5 bags of 80 lb mix with 10% extra. For fence and deck posts, the post itself takes up part of the hole; the fence calculator subtracts it and follows Quikrete's post-setting steps.
How to use this tool
Pick the shape
Slab, strip footing, or a round column or hole.
Enter the size
Length, width and thickness, or diameter and depth, and how many.
Choose the bag
40, 50, 60 or 80 lb, and adjust the waste allowance if you like.
Read the order
Cubic yards and the number of bags, for every bag size side by side.
Questions
How many bags of concrete do I need for a 10x10 slab?
At 4 in thick, about 62 bags of 80 lb mix with 10% extra: 33.3 cu ft of concrete, or 1.36 cubic yards with the extra.
How many 80 lb bags of concrete are in a yard?
About 45: a cubic yard is 27 cu ft and an 80 lb bag of Quikrete Concrete Mix yields about 0.60 cu ft. Add your waste allowance on top.
How many 60 lb bags make a yard of concrete?
About 60, at Quikrete's 0.45 cu ft per 60 lb bag.
How much does a 40 lb bag of concrete cover?
About 0.30 cu ft, which is a 1 sq ft patch about 3.6 in thick.
Should I use bags or ready-mix?
Bags suit small pours like post holes, steps and small pads. For larger slabs, compare the bag count and mixing time with a ready-mix delivery quote; the calculator gives you the cubic yards to ask for.
How do I convert cubic feet to cubic yards?
Divide by 27, because a cubic yard is 3 ft × 3 ft × 3 ft. Ready-mix is ordered by the cubic yard; bags are rated in cubic feet.
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