How to Calculate Channel Weight: Formula and Example

Learning how to calculate channel weight is useful whenever you order MS channel, price a fabrication job or check a supplier’s invoice. A channel, also called a C channel, is not a flat plate or a solid bar, so its weight depends on the shape of its cross-section: the flat web in the middle plus the two flanges sticking out from it. Once you know the depth, flange width and thickness of the section, a short formula gives the weight per metre, and multiplying by the length gives the total weight of the piece. This guide explains that formula in plain terms, works through the same 125 x 65 x 6 mm example shown on the tool page, and answers the questions people ask most about channel weights.

To skip the manual maths, use our free Channel Weight Calculator and enter the depth, flange width, thickness and length to get the weight per metre and the total at once. The rest of this guide shows the same calculation by hand, so you can check any result and understand where it comes from.

The Formula

Weight per metre (kg/m) = cross-section area (mm2) x 0.00785. The 0.00785 factor comes from the standard density of mild steel, 7,850 kg/m3: one square millimetre of section, one metre long, weighs 0.00785 kg. Multiply the area by that factor and you get the weight of one metre of channel.

The cross-section area itself is worked out with a simple approximation: Area (approx) = t x (D + 2 x (B – t)). Here D is the channel depth, or web height, in millimetres, B is the flange width in millimetres, and t is the thickness in millimetres. The formula treats the channel as a flat strip: the web plus the two flanges, with the corner overlap counted only once by subtracting one thickness from each flange. That is why the result is an approximation, not the exact mill weight of a rolled section.

Once you have the weight per metre, the total weight is easy: Total weight (kg) = weight per metre (kg/m) x length (m). Length must be in metres, not millimetres, so divide a length in millimetres by 1,000 first.

How to Calculate Channel Weight Step by Step

1. Identify the section size. Note the depth (D), flange width (B) and thickness (t), all in millimetres, from the supplier’s size chart or the channel marking.
2. Check that all three measurements use the same unit. If any size is given in inches, convert it to millimetres first by multiplying by 25.4.
3. Work out the cross-section area with Area = t x (D + 2 x (B – t)). Remember to subtract the thickness from the flange width before doubling it, so the corners are not counted twice.
4. Multiply the area by 0.00785 to get the weight per metre in kilograms. This factor already includes the mild steel density of 7,850 kg/m3.
5. Multiply the weight per metre by the length in metres for the total weight, and divide by 3.281 if you need the weight per foot instead.

Worked Example

Take the same example shown on the tool page: a channel 125 mm deep, with a 65 mm flange width and a 6 mm thickness, 6 m long. First work out the area: Area = 6 x (125 + 2 x (65 – 6)) = 6 x (125 + 118) = 6 x 243 = 1,458 mm2.

Next, the weight per metre: 1,458 x 0.00785 = 11.45 kg/m (rounded to two decimal places). For the full 6 m length, the total weight is 11.45 x 6 = 68.67 kg. So one 6 m length of 125 x 65 x 6 mm channel weighs about 68.67 kg.

The same method scales easily: a 3 m offcut of the same section would weigh half as much, about 34.34 kg, while a 12 m length would weigh double, about 137.34 kg. If your section is different, only the area changes; the 0.00785 factor stays the same for mild steel.

Common Mistakes / Good to Know

• Using the full flange width twice. The corners where the web meets the flanges belong to both parts, so the formula subtracts one thickness from each flange; skipping that step overstates the area and the weight.
• Mixing millimetres and metres. Depth, flange width and thickness go into the area formula in millimetres, but the length must be in metres when you multiply by the weight per metre.
• Treating the result as an exact ISMC mill weight. Rolled channels have tapered flanges and fillets, so this method gives a close estimate for ordering and costing, not the exact weight on a mill certificate.
• Expecting the supplier’s scale to match exactly. This is a theoretical weight, so small differences from rolling tolerances and the actual thickness are normal; a large gap usually means a wrong size or a mixed-up unit.

Frequently Asked Questions

Once you can weigh a channel on paper, costing a frame or gate becomes much simpler. For flat plates, try the MS Plate Weight Calculator, and read our guide Metal Weight Calculation Formula for Steel, Aluminium and Brass for the density method behind rods, pipes and sheets.