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Concrete Bag Calculator

Find out exactly how many bags of concrete you need for your project. Enter your dimensions below and get instant bag counts for 60lb and 80lb bags — with a built-in waste factor so you don't run short mid-pour.

Concrete Calculator

Select your project type, enter dimensions, and get instant results with bag counts, weight, and cost.

Zone 1

Results

Total Volume

0.00 cu ft

0.00 cu yd

60 lb Bags

0

80 lb Bags

0

Total Weight

0 lbs

(0.00 tons)

Cost Estimate

How to Calculate Concrete Bags Needed

The process is straightforward: calculate your project volume in cubic feet, then divide by the yield per bag. Each bag size covers a different volume:

Bag Coverage (Yield per Bag)

Bag SizeYield (cu ft)Bags per Cu YdBest For
40 lb0.30 cu ft90 bagsSmall repairs, posts
50 lb0.375 cu ft72 bagsFast-setting post holes
60 lb0.45 cu ft60 bagsGeneral DIY projects
80 lb0.60 cu ft45 bagsSlabs, footings, driveways

Quick Reference: Bags Needed by Project

ProjectVolume60lb Bags80lb Bags
1 fence post (4×4)0.65 cu ft21-2
1 fence post (6×6)1.4 cu ft43
8×10 shed pad (4")26.7 cu ft6549
10×10 patio (4")33.3 cu ft8262
10×20 driveway (5")83.3 cu ft204153
20×20 garage (6")200 cu ft489367

Counts include 10% waste factor. Actual yield varies slightly by brand.

60lb vs 80lb Bags: Which to Choose?

  • 60lb bags — easier to carry and mix, better for solo workers and tight spaces (post holes, small repairs)
  • 80lb bags — more cost-effective per cubic foot, fewer bags to open and mix, best for larger projects (slabs, footings)
  • Cost difference: 80lb bags cost ~$0.05 less per cubic foot than 60lb bags
  • Rule of thumb: if you need more than 20 bags, use 80lb to save time and money

Why You Need a Waste Factor

Always add 10% extra to your bag count. Concrete gets lost to:

  • Uneven subgrade and form bulging
  • Spillage during mixing and pouring
  • Concrete left in the mixer or wheelbarrow
  • Over-excavation of post holes

Running short mid-pour creates a cold joint — a weak seam that can crack. It's always better to have 2-3 extra bags than to be 1 bag short.

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Concrete Bags FAQ

How many 80lb bags of concrete make 1 cubic yard?
You need 45 bags of 80lb concrete to make 1 cubic yard. Each 80lb bag yields 0.60 cubic feet, and 1 cubic yard equals 27 cubic feet (27 ÷ 0.60 = 45 bags).
How many 60lb bags of concrete make 1 cubic yard?
You need 60 bags of 60lb concrete for 1 cubic yard. Each 60lb bag yields 0.45 cubic feet, and 1 cubic yard equals 27 cubic feet (27 ÷ 0.45 = 60 bags).
How many bags of concrete do I need for a fence post?
For a standard 4×4 post in a 10-inch diameter hole, 24 inches deep: 1-2 bags of 80lb or 2 bags of 60lb per post. For a 6×6 post in a 12-inch hole, 30 inches deep: 3 bags of 80lb or 4 bags of 60lb per post. Use fast-setting mix if you need the post rigid the same day.
Should I use 60lb or 80lb bags?
Use 80lb bags for slabs, driveways, and any project over 20 bags — they're slightly cheaper per cubic foot and require fewer bags to open and mix. Use 60lb bags when working alone, mixing by hand, or for post holes where 80lb bags would be hard to maneuver. Both produce the same 4000 PSI concrete when cured.
How much area does one 80lb bag cover?
One 80lb bag yields 0.60 cubic feet. For a 4-inch thick slab, that covers about 1.8 square feet (roughly a 16×16 inch area). For a 2-inch thick layer, it covers about 3.6 square feet. Coverage depends entirely on the thickness of your pour.