Bag yield chart
| Bag size | Yield (approx.) | Bags per cubic yard |
|---|---|---|
| 40 lb | 0.30 ft³ | 90 |
| 60 lb | 0.45 ft³ | 60 |
| 80 lb | 0.60 ft³ | 45 |
Yields vary slightly by brand, so check the label on your bag.
Bags or ready-mix?
Bags make sense for jobs under about 1 cubic yard. Beyond that, mixing by hand gets exhausting and joints can form between batches. For larger pours, use our cubic yard calculator and order ready-mix, and compare prices with the concrete cost calculator.
Real example: a 4 × 6 ft shed pad
You are setting a small shed on a 4 inch pad that measures 4 ft by 6 ft. This is a classic bagged-concrete job: small, close to the truck-free zone, and easy to mix in a wheelbarrow.
| Step | Math | Result |
|---|---|---|
| 1. Volume | 4 × 6 × (4 ÷ 12) | 8 ft³ (0.30 yd³) |
| 2. Add 10% waste | 8 × 1.10 | 8.8 ft³ |
| 3. 80 lb bags (0.60 ft³) | 8.8 ÷ 0.60 | 15 bags |
| 3b. 60 lb bags (0.45 ft³) | 8.8 ÷ 0.45 | 20 bags |
| 3c. 40 lb bags (0.30 ft³) | 8.8 ÷ 0.30 | 30 bags |
Same job, three bag sizes. Multiply the bag count by your store's price, and compare the totals, since the cheapest bag size per cubic foot is not always the 80 lb one. An 80 lb bag is also heavy: 15 bags is about 1,200 lb to move and mix, which is a real workout. If that sounds like too much, a small ready-mix order may be worth pricing with the cost calculator.
Another example: setting fence posts
The calculator is built for rectangles, but posts are easy to do by hand. A 10 inch wide hole, 24 inches deep, holds about 1.09 ft³. A 4×4 post (actual size 3.5 in) takes up around 0.17 ft³, which leaves about 0.92 ft³ of concrete per hole, or roughly 1.5 bags of 80 lb. Plan on 2 bags per post. For ten posts, 15 to 16 bags is a safe number.
Mixing tips that save a pour
- Add water slowly. Too much water weakens the concrete, so aim for a stiff, oatmeal-like mix.
- Mix each batch the same way so the color and strength stay consistent.
- Pour in one session. Fresh concrete bonds poorly to concrete that has already started to set.
Bigger than about 1 cubic yard? Switch to the cubic yard calculator, or use the slab calculator for larger patios. The concrete calculator app keeps these numbers in your pocket at the store.
Frequently asked questions
How many 80 lb bags of concrete make a yard?
About 45 bags of 80 lb concrete make one cubic yard, based on a 0.60 cubic foot yield per bag.
How many bags for a 10x10 slab 4 inches thick?
About 56 bags of 80 lb concrete, before adding any waste allowance.
How many bags for a fence post?
It depends on hole size. Use the calculator with the hole's diameter converted to a square footprint, or follow the post manufacturer's guidance.
Is it cheaper to buy bags or ready-mix?
Bags are usually cheaper for very small jobs. For larger volumes, ready-mix is typically more economical and faster.
Take the calculator to the job site
Free concrete calculator app for iPhone and Android.
Google Play App Store