How Much Rebar for a 10x10 Slab?
Rebar to buy
8 sticks
100 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 length10 ft
- Slab width10 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 buy8 sticks
| Slab area | 100 sq ft |
|---|---|
| Bars running the length | 79.5 ft each, spaced across the width |
| Bars running the width | 79.5 ft each, spaced along the length |
| Linear feet, no laps | 133 ft |
| Lap allowance | 0 ft0 splices at 1.67 ft each |
| Total linear feet | 133 ft |
| Sticks at 20 ft | 8160 ft bought, 2 runs cut from one stick |
| Weight | 89 lb0.04 tons |
| Intersections to tie | 49 |
| Chairs | 25one per 4 sq ft |
The material list this produces
| #4 rebar, 20 ft sticks | 8 |
|---|---|
| Tie wire, lb | 1 |
| Chairs | 25 |
| Poly vapor barrier, sq ft | 110 |
Bar spacing compared
Spacing is the one number on this page you actually choose, and it moves everything else. The two right hand columns are total feet and weight. Going from 18 in to 12 in adds 57 ft of steel to a slab this small, which is two more sticks and about a third more money.
| Bar spacing | Rebar to buy | Total linear feet | Weight |
|---|---|---|---|
| 12 in both ways | 10 sticks | 190 ft | 127 lb |
| 16 in both ways | 8 sticks | 152 ft | 102 lb |
| 18 in both ways | 8 sticks | 133 ft | 89 lb |
| 24 in both ways | 6 sticks | 95 ft | 63 lb |
What else matters here
Seven bars each way, 133 ft of steel, and 8 sticks to buy. The last number is the one that catches people out, because 133 divided by a 20 ft stick is 7, and 7 sticks will not build this slab.
The bars are 9.5 ft long rather than 10, because 3 in of cover comes off each end and steel that runs out to the edge of a slab rusts and spalls the corner off. Two 9.5 ft runs fit inside one 20 ft stick with a foot to spare, so the fourteen runs on this slab are cut from 8 sticks and you carry home 160 ft to place 133. Dividing feet by stock length quietly assumes every offcut is usable, and nesting the runs is what a real order does.
Everything else here is small. Eighty nine pounds of steel is two trips from the truck, the 49 intersections take about a pound of tie wire, and 25 chairs hold the mat up off the ground where it does some good. On 100 sq ft the reinforcement is the cheapest part of the pour, and it is the part that decides whether the slab cracks in one straight line you can live with or a web of them you cannot.
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 10x10 slab?
Seven bars each way at 18 in spacing with #4 bar, 133 ft of steel in total, 8 sticks of 20 ft bar and 89 lb.
Why is it 8 sticks and not 7?
Because the runs are nested, not divided. Each run is 9.5 ft after cover, two of them fit in a 20 ft stick, and the fourteen runs come out of 8 sticks. Dividing 133 ft by 20 gives 7 and assumes you can weld the offcuts together.
What spacing should rebar be in a 10x10 patio slab?
#4 at 18 in each way is common residential practice for a four inch slab, and the table below shows what 12, 16, 18 and 24 in each cost. Practice is not code, and the drawing or your local amendment decides.
The rebar calculator takes any dimensions you like and hands back the same list.