The cost of rebar for a concrete slab comes down to how much steel the layout needs, by weight, plus the work to cut, deliver and place it. Bar size and spacing set the weight, so two slabs of the same area can need very different amounts of rebar. The quickest way to an accurate number is to work out the weight from your drawings and have a supplier price it.
This guide walks through what goes into that number, a worked weight estimate you can repeat for your own slab, and the details that make quotes for the "same" slab come out differently.
What you are actually paying for
A rebar price for a slab is rarely one line. It is usually made up of five parts:
- The steel itself. Rebar is bought and sold by weight, so the material cost tracks the total kilograms in the slab.
- Cutting and bending. Most slab mats are straight bar, but edge bars, corner bars, dowels into footings or walls, and any thickened-edge or grade-beam steel add cut and bent pieces.
- Accessories. Chairs or bar supports, tie wire, and sometimes dowel sleeves or caps. These are small items that add up across a large slab.
- Delivery. Distance, truck size and how the load comes off on site.
- Placing. The labour to lay out, support and tie the mat, whether by your own crew or a placing contractor.
When you compare quotes, check which of these each one includes. A low material price that leaves out bent pieces and accessories is not the cheaper option once everything arrives.
The biggest drivers: bar size and spacing
Because steel is priced by weight, bar size and spacing do most of the work in setting the cost.
Bar size. Each step up in size adds a lot of weight per metre. A 15M bar weighs 1.570 kg/m, exactly twice the 0.785 kg/m of a 10M bar. Swap 10M for 15M at the same spacing and the steel weight of the mat doubles. Our rebar size chart lists the weight per metre for every Canadian bar size.
Spacing. Tighter spacing means more bars. Going from 400 mm to 300 mm centres adds roughly a third more bars in each direction.
One mat or two. A single layer at mid-depth is common for lighter slabs. Structural slabs, thick slabs and some heavily loaded floors use a top and bottom mat, which roughly doubles the steel.
Bar size and spacing are design decisions. They come from the structural drawings or, for houses, from your designer and the code requirements that apply to your slab. For how those choices are made, see what size rebar to use for a slab and our guide to rebar spacing in concrete slabs. The examples below are only there to show the arithmetic, not to recommend a layout.
A worked example: estimating slab rebar by weight
Take a 6 m x 8 m slab (about 20 ft x 26 ft) with one mat of bars each way.
Step 1: count the bars in each direction. Divide the width the bars are spread across by the spacing, round up, and add one.
- Bars running the 8 m length, spread across 6 m at 400 mm: 6,000 ÷ 400 = 15 spaces, so 16 bars.
- Bars running the 6 m width, spread across 8 m at 400 mm: 8,000 ÷ 400 = 20 spaces, so 21 bars.
Step 2: total the length. 16 bars x 8 m = 128 m, plus 21 bars x 6 m = 126 m, for 254 m of bar.
Step 3: convert to weight. Multiply by the weight per metre for the bar size.
| Layout (example only) | Total length | Weight per metre | Total weight | Weight per m² |
|---|---|---|---|---|
| 10M at 400 mm each way | 254 m | 0.785 kg | about 199 kg | about 4.2 kg |
| 10M at 300 mm each way | 336 m | 0.785 kg | about 264 kg | about 5.5 kg |
| 15M at 400 mm each way | 254 m | 1.570 kg | about 399 kg | about 8.3 kg |
The same slab carries anywhere from about 200 kg to about 400 kg of steel depending on the layout. That spread is why a flat rate per square foot or per square metre doesn't hold up.
Step 4: add what the simple count misses. A real take-off adjusts for:
- Concrete cover at the edges. Bars stop short of the slab edge by the cover distance, which slightly reduces each bar. The required cover depends on exposure and is set by the drawings and CSA A23.1; see concrete cover for rebar.
- Lap splices. Where a run is longer than the bars you can get, bars overlap. Each lap adds steel, and lap lengths come from the design.
- Openings, sumps and drains. Trim bars around openings add pieces.
- Edge and corner bars, dowels and thickened edges. These are often the bent pieces in a slab order.
- Waste. Cutting stock lengths into your sizes leaves offcuts unless the cutting is planned well.
The same method works for footings and walls: total the length of each bar size, convert to weight, then adjust for laps, cover and waste.
Other things that move the price
Once the weight is known, these details explain most of the difference between quotes.
Order size. Larger orders spread fixed costs (detailing, setup, delivery) over more steel. A small residential slab carries a bigger share of those fixed costs per kilogram.
Straight stock vs fabricated mats. You can buy straight stock and cut it on site, or order bars cut to length and tagged for the slab. Cut-to-length bar costs more in the shop and saves time and waste on site.
Grade and coating. Most slabs use plain (uncoated) 400W bar. Epoxy-coated, galvanized or GFRP bar costs more and is used where corrosion is a concern, such as some parking structures and exposed slabs. Whether your slab needs it is a design call made by the engineer or designer.
Timing and market. Steel prices move with the market. For what is behind those movements in Canada, see what drives rebar prices in Canada.
Site access. A tight urban lot, a backyard pour with no truck access or a delivery that has to be hand-carried takes more time and may need a different truck.
Rebar vs wire mesh vs fibres
People pricing a slab often ask whether mesh or fibres would be cheaper. They can cost less on material, but they are not automatic substitutes:
- Welded wire mesh is quick to roll out, but it is hard to keep at the right depth during the pour. Mesh that ends up on the subgrade does little.
- Fibre-reinforced concrete changes the concrete mix rather than adding a mat. It helps with some cracking issues but is not a like-for-like replacement for structural rebar.
- Rebar is easier to support at the right height and is what most structural and heavier slabs are designed around.
If your drawings call for rebar, a switch to mesh or fibres needs the designer's or engineer's approval. If you're designing a simple slab yourself, check with your building department on what applies.
How to get an accurate slab rebar quote
A supplier can only price what they can see. To get a quote you can rely on, send:
- The drawings or a clear sketch with slab dimensions, thickness and any thickened edges, sumps or openings.
- The reinforcement callout: bar size, spacing, one or two mats, and any dowels or edge bars.
- The site address and access details, so delivery can be priced properly.
- Your schedule, including whether the slab is poured in phases.
- Whether you want supply only or supply and install.
With that, a fabricator can produce a bar list, total the weight and give you a firm price instead of a ballpark.
Get pricing for your slab
We don't publish rebar prices because the number depends on the layout, the order and the current market. Send your drawings or slab details through our quote form and we'll do a free take-off and price it, cut, tagged and delivered across the GTA and Ontario. You can also see the rebar products we supply, from straight bar and dowels to GFRP.
Frequently asked questions
How is the cost of rebar for a slab worked out?
Work out the total length of each bar size from the slab size and spacing, add laps and waste, convert to weight using kg per metre, then add accessories, delivery and placing labour. A supplier prices the material from that weight and the rest from the job details.
How much rebar do I need for a 30 x 40 slab?
It depends entirely on the bar size and spacing on your drawings. As an example only, 10M at 400 mm each way across a 9.1 m x 12.2 m slab works out to roughly 585 m of bar, about 460 kg before laps and waste.
Is there a rebar cost per square foot or per square metre?
Not a fixed one. Steel per square metre changes with bar size and spacing, and doubling the bar size from 10M to 15M at the same spacing doubles the weight. Work out the weight for your layout, then get it priced.
Is wire mesh cheaper than rebar for a slab?
Sometimes on material, but mesh and rebar are not interchangeable by default. Mesh is hard to keep at the right depth during the pour, and the reinforcement type for your slab should come from the drawings or your designer.
Does a 4 inch or 6 inch slab need rebar?
That is a design question, not a thickness rule. Slabs on ground, garage floors and structural slabs are treated differently, so check your drawings or ask your designer or building department before deciding.
