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.
Concrete needed
| Bag size | Bags needed |
|---|---|
| 40 lb | 50 |
| 60 lb | 34 |
| 80 lb | 25 |
| 25 kg | 37 |
| 30 kg | 31 |
At this size
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.
| Run | 20 ft |
|---|---|
| Curb width | 6 in |
| Curb height | 18 in |
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.
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