Bag Calculators
Bag calculators figure out how many bags of concrete you need for a slab, post hole, or sonotube. The three calculators cover the two main bagged-concrete brands (Quikrete and Sakrete) plus a generic concrete-bag calculator that works for either.
Which calculator to use
- Concrete bag calculator — generic, works for any 40/60/80 lb bag. The right answer if you don't care about brand.
- Quikrete calculator — uses Quikrete's published yields. The right answer if you're using Quikrete and want the most accurate bag count.
- Sakrete calculator — uses Sakrete's published yields. The right answer if you're using Sakrete.
For practical purposes, the three calculators give the same answer (Quikrete and Sakrete yields are within 1% of each other at the same bag size). Pick whichever matches the bag on the shelf at your local store.
Bag yield reference
| Bag size | Yield (ft³) | Bags per yd³ | |---|---|---| | 80 lb | 0.60 | 45 | | 60 lb | 0.45 | 60 | | 50 lb | 0.375 | 72 | | 40 lb | 0.30 | 90 |
Bags vs ready-mix
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
- Over 2 yd³: ready-mix wins on price and labor
For a 10×10 ft patio at 4 inches (1.23 yd³), 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.
Post-hole mode
The bag calculators all support post-hole mode: enter the number of holes, the hole diameter, the hole depth, and the post size. The calculator subtracts the post volume automatically and gives you the bag count for the actual concrete needed. See the fence post calculator for the same math with a project-specific workflow.