Two products, two sets of numbers — and why one is not a lighter version of the other
← Back to the calculatorOn a 20 × 40 ft driveway the gap is 916.3 lb, 0.46 ton. Mesh controls cracks in a non-structural slab; bar carries load where the drawing says structural.
The trap is the word “mat”. A mesh mat and a bar mat look like the same idea on a section drawing, but they are counted differently, ordered differently and lapped differently. Read the steel per square foot and the decision makes itself.
Rebar is a deformed round bar sold in 20 ft lengths, counted bar by bar, lapped bar to bar, and cut from stock with an offcut. Welded wire mesh is cold-drawn wire welded into a grid, sold in sheets or rolls, counted by coverage, and overlapped one wire space at the edges. Nothing about the second is a scaled-down version of the first.
That difference shows up in every number on the order. A bar takeoff ends in pieces, feet and pounds. A mesh takeoff ends in sheets, rolls and square feet. The two do not convert without knowing the steel area of the mesh, which is what the W number gives you.
| Welded wire mesh | Rebar | |
|---|---|---|
| Product | Welded wire grid, ASTM A1064 | Deformed bar, ASTM A615 |
| Sold as | Sheets (5 × 10, 8 × 20 ft) or rolls (150 ft) | 20 ft or 40 ft sticks |
| Counted by | Coverage, sheets and laps | Bars, feet, pounds |
| Lap | One wire space + 2 in, min 6 in | Class A or B splice, 1.0 or 1.3 × development length |
| Offcut | Edge trim only | 0 to 40% on 20 ft stock |
| Placement | Floppy, must be lifted and tied | Held at depth by chairs |
Swipe the table sideways for more columns →
This is why “swap the mesh for rebar” is not a sentence an estimator can act on without a number. The swap changes the unit, the lap and the placement, not just the price.
Put both on the same basis and the gap is easy to see. A 100 sq ft area with bars at 12 in on centre both ways holds about 200 ft of bar: 10 ft runs, ten of them each direction. Multiply by the weight per foot and the number falls out.
| Reinforcement | Steel per ft, per direction | lb per 100 ft² | vs 6×6-W1.4 |
|---|---|---|---|
| 6×6-W1.4 mesh | 0.028 in² | 19.1 | 1.0× |
| 6×6-W2.9 mesh | 0.058 in² | 39.5 | 2.1× |
| 6×6-W4.0 mesh | 0.080 in² | 54.5 | 2.9× |
| #3 bar @ 12 in | 0.110 in² | 75.2 | 3.9× |
| #4 bar @ 12 in | 0.200 in² | 133.6 | 7.0× |
| #5 bar @ 12 in | 0.310 in² | 208.6 | 10.9× |
Swipe the table sideways for more columns →
Read the table down the “vs” column and the real point appears: the heaviest common sheet, W4.0, is still less than a #3 bar mat. There is no sheet size that turns into a #4 mat without stacking layers, and stacking layers is a design decision, not a substitution.
Mesh is temperature and shrinkage reinforcement. Its job is to hold a crack closed after the concrete shrinks, so the crack stays hairline instead of opening. That is crack control, and it is a real job — a patio or a shed floor with no steel will crack, and the crack will widen.
Bar is structural reinforcement where the drawing says so: it carries bending and shear that the concrete alone cannot, and it also does the crack-control job because it is steel in the slab. A driveway, a structural slab, a suspended slab — those are bar jobs because the slab is carrying loads, not just holding itself together.
| Slab | Usual answer | Why |
|---|---|---|
| Patio, walkway, shed floor | 6×6-W1.4 mesh, or #3 @ 18 in | Crack control only, foot traffic |
| Driveway, car or truck | #4 @ 18 in, or #4 @ 12 in heavy | Wheel loads, structural |
| Structural slab on grade | Per drawing, usually #4 or #5 | Designed flexural steel |
| Garage floor, basement | #4 @ 12–18 in | Crack control plus point loads |
Swipe the table sideways for more columns →
The mistake that costs money is using mesh where the drawing wanted bar. The slab does not fail the day it is poured; it cracks, deflects and spalls over a season, and by then the mesh is buried and the repair is a replacement.
Mesh wins where the only job is crack control and the slab is not carrying designed loads:
Mesh also wins on speed and handling: a sheet covers 50 sq ft in one lift, and there is no cutting and tying of individual bars. On a small residential pour that is the difference between an afternoon and a day.
What mesh does not win is anything the engineer sized. If the drawing has a bar schedule, the schedule is the answer, and a sheet of mesh laid under it is not a substitute for the bars in it.
Bar wins wherever the slab is doing structural work, and wherever the steel has to be at a set depth:
The depth point is the one people miss. A mat at the bottom of a slab does almost nothing for surface cracks, because the cracks start at the top. Bar on chairs sits in the upper third where the steel can act; mesh, unless it is carefully lifted and tied, does not stay there.
If you are working out a bar mat, the count is on the spacing calculator and the tonnage is on the weight calculator. If you are pricing the two, the difference is the 7× on this page before labour.
The order is where the two products stop looking similar at all. Bar is ordered in sticks and the run length decides the offcut; mesh is ordered in sheets or rolls and the coverage decides the sheet count.
| Bar | Mesh | |
|---|---|---|
| Unit | 20 ft or 40 ft stick | Sheet (5 × 10, 8 × 20 ft) or roll (150 ft) |
| Lap | Class A 1.0 × ld, Class B 1.3 × ld | One wire space + 2 in, min 6 in (8 in at 6 in) |
| Waste | 0–40% depending on how runs divide | Edge trim only |
| Count by | Bars per direction, then sticks | Sheets by coverage, plus lap |
Swipe the table sideways for more columns →
A 20 × 40 ft slab is 800 sq ft. In 5 × 10 ft sheets that is 16 sheets before lap; with an 8 in lap on a 40 ft run you lose about 7% to overlap, so 17 sheets. In bar it is the count on the slab page, then the stick count, then the offcut. Two different arithmetic, two different orders.
A mesh designation has two parts: spacing × spacing, then W number × W number. The W number is the cross-sectional area of one wire in square inches, multiplied by 100.
| Designation | Wire area | Steel per 100 ft² | Typical use |
|---|---|---|---|
| 6×6-W1.4×W1.4 | 0.014 in² | 19.1 lb | Residential slabs, patios |
| 6×6-W2.9×W2.9 | 0.029 in² | 39.5 lb | Light structural, driveways |
| 4×4-W4.0×W4.0 | 0.040 in² | 54.5 lb | Heavier slabs, industrial |
Swipe the table sideways for more columns →
Two names to keep straight: WWF (welded wire fabric) is the older term and WWR (welded wire reinforcement) is the current one. They are the same product, and ASTM A1064 is the specification. A drawing that says “6×6-W1.4 WWF” and one that says “6×6-W1.4 WWR” are asking for the same sheet.
Ask anyone who has pulled up a failed patio and they will tell you where the mesh was: on the ground, under the slab, doing nothing. Mesh has almost no stiffness, so it goes down when it is walked on during placement, and a mat at the bottom cannot control a crack that starts at the top.
Bar does not have this failure mode because chairs hold it at a set height. That is a placement advantage, and it is worth more than the 7× steel difference on a small slab — a light mat at the right depth beats a heavy mat at the bottom.
If you use mesh, the detail is: pull it up as you place, hook it over the form or the chairs, and check it before the screed goes across. If the drawing calls for mesh at mid-depth or in the upper third, that is a placement instruction, not a suggestion.
Two areas, both at 12 in on centre for the bar, so the comparison is the same product choice at two scales.
| Area | 6×6-W1.4 mesh | #4 @ 12 in both ways | Difference |
|---|---|---|---|
| 10 × 10 ft (100 ft²) | 19.1 lb | 133.6 lb | 114.5 lb |
| 20 × 40 ft (800 ft²) | 152.5 lb | 1,068.8 lb | 916.3 lb |
Swipe the table sideways for more columns →
That is the number to carry into a quote. At a material price per pound the difference is real money, and it is the reason a builder reaches for mesh on a patio and bar on a driveway — not habit, arithmetic.
No, at the sizes people compare. A 6x6-W1.4 sheet puts 19.1 lb of steel in 100 sq ft and #4 bar at 12 in on centre puts 133.6 lb, so the bar mat has about seven times the steel. Strength is not the only measure - mesh is doing crack control, bar is doing structural reinforcement - but the two are not interchangeable by area of steel.
On a light-duty driveway that only sees foot traffic or a garden cart, mesh is a common crack-control choice. On a driveway that takes cars, trucks or a camper, the usual answer is deformed bar at the spacing on the drawing, because the slab is carrying wheel loads. If a drawing specifies bar, the drawing wins.
6x6 is the wire spacing in inches both ways. W1.4 is the wire size: a W number is the cross-sectional area of the wire in square inches multiplied by 100, so W1.4 is 0.014 sq in. The full designation 6x6-W1.4xW1.4 says the same wire runs in both directions.
A 6x6-W1.4xW1.4 sheet carries about 0.028 sq in of steel per foot in each direction, which is 19.1 lb per 100 sq ft. Heavier sheets go up from there: 6x6-W2.9 is about 39.5 lb per 100 sq ft and 6x6-W4.0 is about 54.5 lb.
At #4 bar, 12 in on centre both ways, 800 sq ft takes 1,068.8 lb. At 6x6-W1.4 mesh it takes 152.5 lb. The difference is 916.3 lb, or 0.46 ton - and that is the whole reason the two are not a swap.
No. One or the other, as the drawing says. Putting mesh under a bar mat does not make the slab stronger in any way an engineer counts; it adds a second layer that can end up at the wrong depth. If the drawing calls for both, that is a specific detail, not a default.
One wire space plus 2 in, and never less than 6 in. At 6 in spacing that is an 8 in lap. Mesh laps are shorter than bar laps because the wire is small and continuous, but the lap still has to be wired or tied so the sheets do not separate while the concrete is placed.
Because it is floppy. A sheet of mesh has almost no stiffness, so when it is walked on during placement it goes down, and a mat at the bottom of the slab does nothing for cracks that start at the surface. Bar on chairs holds its depth, and that placement is a bigger difference than the weight of steel.
No. Rebar is a deformed round bar sold in 20 ft lengths and lapped bar to bar. Welded wire mesh is cold-drawn wire welded into a grid and sold in sheets or rolls, with no 20 ft stock length and no offcut in the same sense. The only thing they share is that both are steel in concrete.
Nothing physical. Welded wire fabric (WWF) is the older name; welded wire reinforcement (WWR) is the current one, and both refer to the same welded grid. ASTM A1064 is the specification that covers the wire.