Per unit
Each foot of this plain curb holds 0.75 ft³, so one cubic yard pours about 36 ft of it.
One 80 lb bag fills about 10 in of run.
Change the dimensions in the curb calculator. Why every count rounds up: how many bags of concrete you need.
Curb
Concrete for a 20 ft curb
A 20 ft run of plain curb, 6 in wide and 18 in tall. The volume is the curb cross-section times the run. That is 15 cubic feet, or 0.56 cubic yards: 25 bags of 80 lb premix or 34 bags of 60 lb, before any waste.
Concrete needed
0.56cubic yards· 0.425 m³· 15 ft³
| Bag size | Bags needed |
|---|---|
| 40 lb | 50 |
| 60 lb | 34 |
| 80 lb | 25 |
| 25 kg | 37 |
| 30 kg | 31 |
Planning estimate, with no waste allowance included. Add 5-10% for spillage and over-excavation, and check the yield printed on your bag. Structural work must follow your local building code and an engineer's specification.
Bagged or ready-mix?
Bags
0.56 yd³ is under a ready-mix supplier's usual one-yard minimum, so bags are the answer whatever the price per yard says. Buy a couple more than the count above and return what you do not open.
Same job, other sizes
Plain curb
| Size | ft³ | yd³ | yd³ to order (+10%) | 80 lb bags (+10%) | 60 lb bags (+10%) |
|---|---|---|---|---|---|
| 20 ft run (this page) | 15 | 0.56 | 0.61 | 28 | 37 |
| 50 ft run | 37.5 | 1.39 | 1.53 | 69 | 92 |
| 100 ft run | 75 | 2.78 | 3.06 | 138 | 184 |
At this size
What changes on a 20 ft curb
Mixing or ordering it
25 × 80 lb bags is 0.56 yd³, which is about 13 batches in a 6 ft³ site mixer at two bags a batch. That is a comfortable half-day for two people - one mixing, one placing - and at 0.56 yd³ you are under the one-yard minimum most ready-mix suppliers will deliver, so bagging it is the route regardless of price.
The dimensions used
| Run | 20 ft |
|---|---|
| Curb width | 6 in |
| Curb height | 18 in |
How it is worked out
A curb is a long prism: its cross-section (width × height) times the run. For curb-and-gutter, the flat gutter pan (width × thickness) is added to the cross-section before multiplying by the length.
That volume - 15 ft³ - is divided by 27 to give 0.56 cubic yards, and by each bag's yield to give the bag count. An 80 lb bag of premix yields about 0.60 cubic feet, so this job takes 25 of them; bag counts always round up, because you cannot buy part of a bag.
Ordering ready-mix instead? Suppliers sell by the cubic yard (or cubic metre) and usually have a minimum load and a short-load surcharge - worth a call before you choose between bags and a truck.
Formwork
What is being measured
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