Concrete Bag Calculator
Free concrete bag calculator. Enter slab size, get 40, 60, and 80 lb bag counts and equivalent cubic yards. Post-hole mode included. No sign-up, mobile-friendly.
Bag counts by cubic yard
One cubic yard of concrete equals 45 × 80 lb bags, 60 × 60 lb bags, or 90 × 40 lb bags of mix. The table below rounds up to the nearest whole bag for common yardage.
| Volume | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|
| 0.25 yd³ | 11 | 15 | 23 |
| 0.5 yd³ | 23 | 30 | 45 |
| 1 yd³ | 45 | 60 | 90 |
| 1.5 yd³ | 68 | 90 | 135 |
| 2 yd³ | 90 | 120 | 180 |
| 3 yd³ | 135 | 180 | 270 |
| 4 yd³ | 180 | 240 | 360 |
| 5 yd³ | 225 | 300 | 450 |
| 6 yd³ | 270 | 360 | 540 |
| 8 yd³ | 360 | 480 | 720 |
| 10 yd³ | 450 | 600 | 900 |
Slab vs post-hole mode
For a flat slab, the calculator above is the right tool — pick a rectangle, enter length, width, and depth. For fence post holes or sonotubes, switch the calculator to "Post holes" mode — it subtracts the post or tube volume automatically.
Concrete bag calculators answer the most-asked DIY question: how many bags of concrete do I need? This page figures it three ways — 40 lb bags (the cheap ones, for small jobs), 60 lb bags (the middle option), and 80 lb bags (the standard, the right answer for most slabs).
One cubic yard of finished concrete = 45 × 80 lb bags, 60 × 60 lb bags, or 90 × 40 lb bags. A 10×10 ft slab at 4 inches thick needs 1.23 yd³ of concrete, which is 56 × 80 lb bags, 74 × 60 lb bags, or 111 × 40 lb bags.
How to use this calculator
Switch between Dimensions mode (enter length, width, depth) and Post holes mode (number of holes, diameter, depth, post size). The bag table below rounds every count up so you never come up one bag short.
Bags vs ready-mix — when to switch
The math is straightforward: bags get uneconomical fast as the pour grows. A typical pricing crossover:
- Up to 1 yd³: bags are usually cheaper (no truck minimum, no short-load fee)
- 1 to 2 yd³: roughly even, depends on region and how much help you have
- Over 2 yd³: ready-mix wins on price and labor — wheelbarrowing 60+ 80 lb bags is back-breaking
For a 10×10 ft patio at 4 inches, you're at 56 bags. That's 4,480 lb of mix to haul, mix, and pour. Most homeowners should rent a mixer or call a ready-mix plant for pours over ~30 bags.
How concrete bag yields are calculated
Each bag's yield comes from the manufacturer. An 80 lb Quikrete or Sakrete bag yields about 0.60 ft³ of finished concrete. A 60 lb bag yields 0.45 ft³. A 40 lb bag yields 0.30 ft³. These numbers are stamped on every bag. We multiply by 1 bag's worth of ft³ to get a bags-per-yard figure (45 for 80 lb, etc.), then ceil the final bag count to the nearest whole bag.
Common mistakes
- Forgetting waste: 10% extra covers spillage, over-excavation, and the inevitable short-pour at the end. The calculator defaults to 10%.
- Cold joints on big pours: concrete starts setting in 30–60 minutes. If you can't place and finish a pour inside that window, you have too much to bag-mix. Split into sections or call ready-mix.
- Wrong water ratio: more water makes concrete easier to pour but reduces final strength dramatically. Follow the bag's water ratio exactly — usually 3–4 quarts per 80 lb bag. Sloppy water = weak, cracked slab.