Stainless Steel Coil Guide 2026: ID, Weight, Slitting and Cut-to-Length

A stainless steel coil is bought on four numbers: inside diameter, weight, width and edge condition. Miss one and the coil sits in your yard. The standard ID is 508 mm (20 inch), with 610 mm (24 inch) for Japanese and some European lines, and cold rolled export coils normally run 3 to 8 tonnes with 4 to 6 tonnes most common. For 304, one square metre weighs thickness × 7.93 kg, so a 1 mm coil is 7.93 kg/m². This guide covers the specs, the 2026 prices and the loading math.

What Does a Coil Specification Actually Look Like?

A coil quote without these five lines is incomplete: grade, finish, thickness, width, and ID. Add edge condition and coil weight and you have the full picture.

Why the Coil ID Matters More Than Buyers Expect

The ID has to match your uncoiler mandrel. A 610 mm coil will not sit on a 508 mm mandrel, and a 508 mm coil on a 610 mm line needs adapter segments that many factories do not have.

I have seen a full container of 316L rejected for exactly this. The buyer's leveling line was built for 610 mm and the coil came on 508 mm eyes. Nothing was wrong with the steel. It just did not fit the machine.

Ask your production manager for the mandrel size in millimetres and put it on the purchase order. If you buy through a trader, confirm it in writing twice.

How Do You Calculate Coil Weight and Length?

The formula is the same one used for sheet, applied to the running length of the coil. Weight (kg) = length (m) × width (m) × thickness (mm) × density. Density is 7.93 g/cm³ for 304 and 304L, 7.98 for 316 and 316L, and 7.70 for 430.

In practice you work backwards: you know the coil weight you want, so you solve for length.

Use that table to sanity check a supplier. If someone offers you a 5 t coil of 3 mm at 400 m of length, the numbers do not work.

For 316L add about 0.6% to every figure, and for 430 subtract about 2.9%. Those are small percentages, but they add up on a 20 t order.

304, 304L and 316L Coil Prices in September 2026

China mill prices for the week of 11 September 2026 are a useful benchmark for any negotiation, wherever you buy. All figures are USD per tonne.

Three things jump out of that table. 304L costs only about 1.6% more than 304 on hot rolled, so if your product is welded heavily there is little reason to skip the low-carbon grade.

Thin gauges cost more, not less: 0.3 mm 304 2B is USD 139 per tonne above 1.0 mm because of the extra rolling passes. And 316L is more than double 304 hot rolled at USD 4,708 against USD 2,309, which is the molybdenum and nickel content doing the talking.

Mill Edge vs Slit Edge: Pick Before You Order

Mill edge is the original rolled edge. The coil is full width, the edge is smooth with a slight crown, and it is the cheaper option because no extra processing is involved.

Slit edge comes from running the coil through a slitting line to cut it to a narrower width. The edge is straighter and more uniform, but you get a small burr and occasionally a slight camber that shows up when you feed a long line.

Tube mills, roll formers and anyone feeding a continuous line usually want slit edge at an exact width. Buyers who cut their own blanks often take mill edge and trim it in house, because paying slitting charges and then trimming again is wasted money.

Coil or Cut Sheet: Which Should You Order?

Coil is normally cheaper per tonne than sheet of the same grade and finish, because the processor has not run a leveling and cut-to-length line yet. That processing typically adds something in the region of USD 40-80 per tonne, so ask your local processor for the real number in your market.

Coil only makes sense if you have the equipment or a reliable toll processor. If you buy coil and then pay someone else to level and cut it, the saving usually shrinks to a couple of percent, and you carry the coil handling risk yourself.

If your parts come off a fiber laser cutting machine, do the math on both routes. Sheared blanks from cut sheet sometimes beat coil once you count the offcuts and the space a coil line takes up in the shop.

Container Loading: How Many Coils Fit?

A 20ft GP takes about 24,000 to 25,000 kg of stainless coil after dunnage and strapping. That is four to five cold rolled coils at 5 t each.

Coils ship eye to sky, standing on their edge, blocked with wooden dunnage and steel strapping so they cannot roll. Never let a loader drop a coil flat onto its side and call it secured, because that is how side walls get pushed out.

Two practical notes. First, a 40ft box gains volume but almost no payload, so heavy coil orders stay in 20ft units. Second, if you mix coil with sheet in one container, put the coil over the axles and brace the sheet around it, and make sure the total stays inside the payload limit rather than the gross limit.

Storage and Handling Mistakes That Show Up as Claims

Condensation between wraps. A cold coil moved into a warm humid warehouse sweats under its own wrapping. That is where white rust stains come from, and buyers blame the mill for something storage caused. Let coils come to room temperature before you open them.

Lifting through the eye with bare tines. A forklift tine will scratch the inside wrap and, on a heavy coil, bend the eye. Use a coil boom or a C-hook.

Stacking 2B coils on their sides. It looks efficient until the outer wraps get dented, and dented 2B coil becomes reject material for any visible application.

Frequently Asked Questions

Written by David Chen, Sales Engineer at FANY LASER. Connect on LinkedIn for stainless steel and aluminum sourcing, price data and market updates.