How Much Rebar for a 40x60 Slab?
Rebar to buy
169 sticks
2,400 sq ft, #4 bar at 18 in both ways, 3 in cover, 20 ft sticks, 40 diameter lap splices.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Slab length40 ft
- Slab width60 ft
- Bar spacing, both ways18 in
- Bar size#4, 1/2 in
- Cover from the edge3 in
- Bar stock length20 ft
- Lap splice40 bar diameters
Rebar to buy169 sticks
| Slab area | 2,400 sq ft |
|---|---|
| Bars running the length | 4039.5 ft each, spaced across the width |
| Bars running the width | 2759.5 ft each, spaced along the length |
| Linear feet, no laps | 3,186.5 ft |
| Lap allowance | 170 ft102 splices at 1.67 ft each |
| Total linear feet | 3,356.5 ft |
| Sticks at 20 ft | 1693,380 ft bought, 102 splices, offcuts carried into the next run |
| Weight | 2,242 lb1.12 tons |
| Intersections to tie | 1,080 |
| Chairs | 600one per 4 sq ft |
The material list this produces
| #4 rebar, 20 ft sticks | 169 |
|---|---|
| Tie wire, lb | 8 |
| Chairs | 600 |
| Poly vapor barrier, sq ft | 2,640 |
Bar spacing compared
Spacing swept at 40 by 60 ft. The right hand column is intersections to tie: 2,400 ties at 12 in against 600 at 24 in.
| Bar spacing | Rebar to buy | Total linear feet | Intersections to tie |
|---|---|---|---|
| 12 in both ways | 251 sticks | 5,001.7 ft | 2,400 |
| 16 in both ways | 188 sticks | 3,750.8 ft | 1,350 |
| 18 in both ways | 169 sticks | 3,356.5 ft | 1,080 |
| 24 in both ways | 126 sticks | 2,501.7 ft | 600 |
What else matters here
Two thousand two hundred and forty two pounds is 1.12 tons of #4 bar, 169 sticks, and 1,080 intersections to tie.
Bar size moves the weight far more than the stick count. Going from #3 to #8 on this slab moves the stick count from 166 to 178, about seven percent. It moves the weight from 1,245 lb to 9,496, which is more than seven times. So on a slab this size the bar size decides the tonnage and barely touches the stick count.
The second decision is spacing, in the table below. At 12 in this slab wants 251 sticks and 2,400 ties; at 24 in it wants 126 and 600. Which spacing is right is not a material question: the engineer, the drawing or the local amendment decides it. What this page is for is knowing the size of the order before the quote lands.
What this calculator assumes
- Bars are figured as a grid running both ways at the same spacing, which is how a residential slab, a driveway and a footing mat are normally drawn.
- Weights are the published ones: #3 is 0.376 lb per foot, #4 is 0.668, #5 is 1.043, #6 is 1.502, #7 is 2.044 and #8 is 2.670.
- The stick count is nested, not divided. When a run fits inside a stock bar, the count says how many runs are cut from one stick and never splices a bar that did not need splicing. When a run is longer than a stock bar it is built from a chain of sticks with a lap at every joint, and the offcut from one run starts the next. That is why the stick line and the linear feet line never agree, and the gap between them is the offcut you pay for.
- A 40 diameter lap is the common residential rule of thumb. ACI 318 sets the real development length from the concrete strength, the bar position and the cover, and an engineered drawing overrides anything on this page.
- Chairs are one per four square feet, which keeps the mat off the ground on an ordinary pour. Wet setting bar into poured concrete is a different method and this list does not price it.
Questions people ask
How much rebar for a 40x60 slab?
40 bars one way and 27 the other at 18 in with #4 bar, 3,356.5 ft including the laps, 169 sticks of 20 ft steel and 2,242 lb.
How much does the rebar in a 40x60 slab weigh?
2,242 lb at #4 and 18 in spacing, which is 1.12 tons. At #8 the same mat weighs 9,496 lb, so the bar size moves the weight far more than the spacing does.
How much vapor barrier does a 40x60 slab need?
The material list carries 2,640 sq ft of poly against 2,400 sq ft of slab.
The rebar calculator takes any dimensions you like and hands back the same list.