Concrete Bag Calculator
Find how many bags of concrete you need, in every common bag size.
Measure your project
Your answer
That is 8.8 cubic feet. We added 10% extra.
If you buy bags
One 80 lb bag makes 0.6 cubic feet of concrete.
If you order a truck (ready-mix)
Ask for 0.50 cubic yards. We round up to the next quarter yard.
This answer is a guide. For footings, driveways or anything that holds weight, check your local building rules or ask a builder or engineer.
Which costs less?
But you must mix 15 bags by hand. That is 0.6 tons. For a big job, a truck saves a lot of hard work.
Prices are US middle prices from October 2026. Ask your store for their price.
Quick answers
- What one bag makes
- 90 lb: 0.675 cubic feet · 80 lb: 0.6 cubic feet · 60 lb: 0.45 cubic feet · 50 lb: 0.375 cubic feet · 40 lb: 0.3 cubic feet
- The bags for one cubic yard weigh
- About 3,600 lb of dry mix, or 1.8 tons. That is the same for every bag size.
- One 80 lb bag covers
- About 1.8 sq ft at 4 in thick.
- One cubic yard in 80 lb bags costs
- About $292, at our middle price of $6.49 a bag.
How to work it out
- Work out the cubic feet: length × width × thickness, all in feet.
- For post holes, add "Round holes" in step 1 of the calculator.
- Add 10% extra.
- Divide by what one bag makes. An 80 lb bag makes 0.6 cubic feet.
- Round up to whole bags.
6 × 4 × 0.333 = 8 cubic feet
8 + 10% = 8.8 cubic feet
8.8 ÷ 0.6 = 14.7 → 15 bags of 80 lb
Bags for posts and small pads
This table shows bags for some small jobs, in four bag sizes. Each count has 10% extra. We round up to whole bags.
| Job | 40 lb | 50 lb | 60 lb | 80 lb |
|---|---|---|---|---|
| Post hole 8 in wide, 24 in deep | 3 | 3 | 2 | 2 |
| Post hole 10 in wide, 30 in deep | 5 | 4 | 4 | 3 |
| Post hole 12 in wide, 36 in deep | 9 | 7 | 6 | 5 |
| Pad 2 × 2 ft, 4 in thick | 5 | 4 | 4 | 3 |
| Pad 3 × 3 ft, 4 in thick | 11 | 9 | 8 | 6 |
| Pad 3 × 5 ft, 4 in thick | 19 | 15 | 13 | 10 |
| Pad 4 × 6 ft, 4 in thick | 30 | 24 | 20 | 15 |
We count the whole hole, post included.
For bags per post, see our fence post concrete calculator.
Pads are 4 in thick here. That is the least a town building guide asks for a patio or path.
Odd shape? Split it into boxes. Add each one as a slab.
Big bags or small bags?
Small bags are easier to lift. But you need more of them.
The total weight does not change. The dry mix for one cubic yard, in 45 bags of 80 lb, weighs 3,600 lb. In 90 bags of 40 lb, it weighs 3,600 lb.
Small bags can cost more for the same amount. At our middle prices, a cubic yard in 80 lb bags costs about $292. In 40 lb bags, it costs about $512.
The 80 lb price is the middle of 9 stores. The 40 lb price comes from only 3 stores, so treat it as a rough guide.
| Bag size | At 4 in thick | At 5 in thick |
|---|---|---|
| 90 lb | 2 sq ft | 1.6 sq ft |
| 80 lb | 1.8 sq ft | 1.4 sq ft |
| 60 lb | 1.4 sq ft | 1.1 sq ft |
| 50 lb | 1.1 sq ft | 0.9 sq ft |
| 40 lb | 0.9 sq ft | 0.7 sq ft |
Worked out from what Quikrete says each bag makes.
Fast-setting or regular mix?
Quikrete also sells Fast-Setting Concrete Mix (No. 1004). It comes in 50 lb and 60 lb bags.
Each bag makes the same amount as a regular bag of the same weight. So your bag count stays the same.
For a 3 in square post, Quikrete calls for 2 bags of 50 lb. That hole is 9 in across and 30 in deep.
Filling around the post to the top would take about 3 bags. But Quikrete stops 3–4 in below the top and fills the rest with soil. That explains most of the gap.
It can cost more. One store in Ohio sold the 50 lb bag for $13.99, about $37 per cubic foot.
Regular mix in 80 lb bags is about $11 per cubic foot, at our middle price. The Fast-Setting price is from one store only, so check yours.
How to read the bag
Check the name on the bag before you buy. Concrete mix, cement and mortar are not the same thing.
- Concrete mix is ready to use. The label says how much concrete one bag makes. Quikrete Concrete Mix is No. 1101.
- Portland cement is just one part of concrete. To mix your own, Quikrete suggests 1 part cement, 2 parts sand and 3 parts gravel. One cubic yard then takes 5 to 6 bags of 94 lb cement.
- Mortar mix is for laying blocks and bricks. One 80 lb bag of Quikrete Mortar Mix lays up to 13 blocks. For walls, use our concrete block calculator.
Brands we checked agree. A Sakrete bag makes the same amount as a Quikrete bag of the same weight. Sakrete just rounds its 50 lb bag to 0.38 cubic feet. Quikrete says 0.375.
Before you go to the store
- Measure across each hole and how deep it is, in inches. Measure pads in feet.
- Put your sizes in the calculator. Note the count for the bag size your store sells.
- Keep the 10% extra. It covers spills and uneven ground.
- Check the weight. The 4 × 6 ft pad above takes 15 bags of 80 lb. That is 1,200 lb to lift.
- Buy all the bags in one trip, so you don't run out halfway.
Questions people ask
How many bags of concrete do I need?
Find the cubic feet of your hole or pad, then add 10%. Divide by what one bag makes, and round up. The calculator above shows every bag size at once.
How much concrete does a 90 lb bag make?
About 0.675 cubic feet. You need 40 of them for a cubic yard.
How many yards is an 80 lb bag of concrete?
About 0.022 cubic yards. One bag makes 0.6 cubic feet, and a cubic yard is 27 cubic feet.
How many bags of concrete make a yard?
45 bags of 80 lb. Or 60 bags of 60 lb, 72 of 50 lb, or 90 of 40 lb.
How many bags of concrete are in a cubic foot?
About 1.7 bags of 80 lb. Or 2.2 bags of 60 lb, or 3.3 of 40 lb. You can only buy whole bags, so round up.
How many feet does a bag of concrete cover?
An 80 lb bag covers about 1.8 sq ft at 4 in thick. A 60 lb bag covers about 1.4 sq ft. The table above shows the other sizes.
How much is a bag of concrete?
About $6.49 for an 80 lb bag. That is the middle price of 9 US stores in Oct 2026. A 40 lb bag is about $5.69. But we found only 3 store prices for it, and could check only 2 again.
Where our numbers come from
- Bag sizes and weight: Quikrete Concrete Mix data sheet
- Fast-Setting mix: Quikrete data sheet (bag sizes and fence posts)
- Bag sizes: Sakrete bag data (checked Oct 2026)
- Bag sizes: Sakrete 5000 Plus bag data (rounds 50 lb to 0.38 cubic feet)
- Extra for spills: Sakrete slab calculator (10%)
- How thick: a town building handout (Palatine, IL)
- How thick: a ready-mix maker's driveway guide
- Cement per cubic yard: Quikrete Portland Cement data sheet (5 to 6 bags of 94 lb)
- Mortar per block: Quikrete Mortar Mix data sheet
- Bag price: the middle price of 9 US stores (Oct 2026)
- 40 lb bag price: the middle of 3 US stores (Oct 2026; few prices, one not checked again)
- Fast-Setting bag price: one store in Ohio (Oct 2026; a single price)
- Truck price: the middle price of 5 US concrete sellers (Oct 2026)
- Small-order fee: the middle of 4 US cost guides (2026)
Made by BuildersCount. Last checked 3 Oct 2026.
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