Binding wire gauge: SWG, BWG and mm sizes

Key facts

• Binding wire and tie wire are trade names for soft, black annealed steel wire.
• A higher gauge number means a thinner wire in BWG, SWG and the US Steel Wire Gauge.
• The same gauge number gives a different diameter in each of these systems, so the diameter in mm is what an order should state.
• The mass of a round steel wire is π/4 × d² × ρ, taking the density of steel as 7850 kg/m³.
• Black annealed wire is quoted from 0.8 to 8 mm in diameter, to EN 10218-2.

What gauge is binding wire?

There is no single answer, because the name does not come from a standard. Binding wire is what site crews and hardware buyers call a soft wire for tying and fixing, and our product data lists it as another name for black annealed wire. Annealing is a heat treatment that metallurgy references describe as raising ductility and lowering hardness, which is why the wire twists by hand. “Binding wire” and “tie wire” are two labels for that one product, not two products.

What differs between buyers is the size, usually written as a gauge number: 16, 18, 20. We found no source that ties the name to one gauge, so we do not say which gauge a job needs. We can show what each number means in millimetres.

Why does the gauge system matter?

A gauge number is an index into a table, and there is more than one table. In each a higher number means a thinner wire, but the diameters differ.

• SWG, the Standard wire gauge, is the British gauge, defined in BS 3737 and described as an Imperial unit for wire diameters.
• BWG, the Birmingham wire gauge, is listed by Engineering ToolBox as Birmingham iron wire, and by NIST as the Stubs’ wire gage.
• US Steel Wire Gauge is the gauge that NIST and Engineering ToolBox list for steel wire, also known as Washburn & Moen. NIST notes that it should not be abbreviated SWG, to keep it apart from the British one.
• AWG, the American wire gauge, is a system for round, solid, nonferrous, electrically conducting wire, with its dimensions given in ASTM B 258. It is also known as Brown & Sharpe, and its numbers must not be read from the steel wire columns.

So “18 gauge” can be four different wires. A quick test: 20 gauge is under 1 mm in BWG, SWG and the Steel Wire Gauge alike, so a listing that pairs 20 gauge with a size of several millimetres is wrong in all three.

Binding wire gauge to mm: size chart

The diameters are those of our wire gauge chart. BWG and Steel Wire Gauge values were checked against NIST and Engineering ToolBox, SWG values against NIST and Wikipedia.

How to read it:

• 18 gauge is about 1.2 mm in all three, but the third decimal differs: 1.245 mm in BWG against 1.219 mm in SWG. In AWG, 18 is 0.0403 inch, about 1.02 mm, a visibly thinner wire.
• 16 gauge runs from 1.600 to 1.651 mm, and 20 gauge from 0.889 to 0.914 mm.
• 22 gauge is between 0.711 and 0.737 mm, below the 0.8 mm lower end of our range.

The Steel Wire Gauge values rest on the inch figures that NIST and Engineering ToolBox agree on. NIST gives finer decimals for some gauges, so a small gap between two charts does not mean one is wrong.

How many metres are in 1 kg of binding wire?

Buyers who ask for binding wire by the kilogram are really asking how long a coil is. One metre of round wire weighs π/4 × d² × ρ, with d in metres. Engineering ToolBox lists steel at 7850 kg/m³, and Wikipedia gives the usual range as 7750 to 8050 kg/m³. The table uses 7850, as does our wire weight calculator.

For the gauges above: 18 gauge holds about 105 m in one kilogram in BWG and about 109 m in SWG, and 16 gauge about 60 m in BWG and 61 m in SWG. Doubling the diameter makes the wire four times heavier per metre.

These are theoretical masses of bare steel. They leave out the diameter tolerance, which EN 10218-2 sets for round wire, and the packing. The mass on the packing list is the final figure.

Black annealed or galvanized?

The size question is the same for both finishes. Black annealed wire is uncoated. Galvanized wire carries a zinc coating, useful where the tied wire sits outdoors or in damp air, and is quoted in the same 0.8 to 8 mm range with a coating of 50 to 300 g/m². Our comparison of black annealed vs galvanized tie wire helps when the finish is undecided. Zinc adds mass beyond the table above, so ask for the coil weight.

What should a binding wire request state?

Give the size in a form that cannot be misread, then the rest of the order.

1. Diameter in mm. One figure per item, such as 1.2 mm, with the gauge in brackets if your customer used one: “1.2 mm (18 SWG)”.
2. Finish. Black annealed or galvanized. For galvanized, add the coating figure in g/m².
3. Standard. We quote black annealed wire to EN 10218-2, which sets the diameter tolerance.
4. Coil or roll weight and packing. If you have no preference, ask each offer for its usual packing. The load per container is confirmed per order; the container loading guide explains the limits.
5. Quantity. Tonnes, per diameter.
6. Destination. The port and the Incoterms rule you want.

Our binding wire guide for importers covers a full order, and the tie wire guide both finishes.

Can binding wire be quoted for the UAE or Nigeria?

Yes. Importers in the United Arab Emirates and Nigeria send the same request (see binding wire for UAE importers and for Nigeria importers): size in mm, finish, quantity, packing and port. Duties, clearance and documents depend on the destination, so confirm them with your customs broker before you order.

How does Reinwent handle a request?

Reinwent is a trading and sourcing company, not a mill. We collect offers from several suppliers on your specification, set them on one basis and stay in contact until delivery; the how we work page lists each step. Some products are available from stock. Black annealed wire from Türkiye describes that supply route, and what is annealed wire covers the heat treatment. For the jobs, see black annealed wire uses.

When the diameter in mm, finish, quantity, packing and port are ready, request a quote and you receive a quotation within 12 hours.