Material Summary
- Total rebar—
- With waste + lap—
- Sticks to buy—
- Approx. weight—
- Estimated cost—
Rebar Size Chart
| Size | Diameter | Weight | Lap (40d) |
|---|---|---|---|
| #3 | 3/8 in | 0.38 lb/ft | ~15 in |
| #4 | 1/2 in | 0.67 lb/ft | ~20 in |
| #5 | 5/8 in | 1.04 lb/ft | ~25 in |
| #6 | 3/4 in | 1.50 lb/ft | ~30 in |
Spacing Guide by Project
| Project | Typical bar + spacing |
|---|---|
| Patio / sidewalk | #3 to #4 at 16 to 18 in, two-way |
| Driveway / slab | #4 at 12 to 18 in, two-way |
| Footing | #4 to #5, 2 to 3 continuous bars |
| Retaining / stem wall | #4 to #5 at 12 to 24 in, vertical + horizontal |
How Much Rebar Do I Need?
Rebar is laid out on a spacing, so the quantity comes from the area or wall and the bar spacing, not a single number. For a slab grid you count the bars each way: the slab dimension divided by the spacing, plus one, gives the number of bars, and each bar spans the other dimension. Add the two directions for a two-way grid. This calculator does that for slabs, footings, and walls, then adds a waste and lap allowance and converts the total into sticks to buy, because no supplier sells you 486 loose feet of rebar.
Rebar Sizes and Spacing
Rebar size is given in eighths of an inch: a #4 bar is four eighths, or one half inch. Residential slabs and footings commonly use #3, #4, or #5. Spacing is chosen by the engineer, but 12 to 18 inches on center is typical for slabs, with tighter spacing for heavier loads. Closer spacing and bigger bars both add steel, so the size and spacing presets here let you compare options quickly and see the stick count change.
Buying Rebar by the Stick
Rebar is sold in fixed lengths, most often 20 foot sticks, sometimes 10, 40, or 60. Because runs longer than a stick must be spliced with an overlap, real projects always need more than the bare linear footage. A 10 percent allowance covers both the laps and the offcuts for most jobs; tight, heavily spliced layouts may want 15 percent. The calculator rounds up to whole sticks and estimates the cost and weight so you know what is going in the cart and the truck.
Frequently Asked Questions
How much rebar for a slab? Count bars each way: dimension divided by spacing plus one, times the opposite dimension, for both directions.
What size rebar for a driveway? Commonly #4 at 12 to 18 inches on center in a two-way grid.
How long is a stick of rebar? Most often 20 feet, with 10, 40, and 60 foot lengths also available.
How much should I add for laps? About 10 percent for typical jobs, since each splice overlaps roughly 40 bar diameters.