C8x18.75 — Dimensions, Weight & Section Properties
American Standard (C) channel per ASTM A6 / AISC Steel Construction Manual
C8x18.75 is an American Standard steel channel 8 inches (203.2 mm) deep with a 2.53 in (64.3 mm) flange, weighing 18.75 pounds per foot (27.9 kg/m) — that is what the "18.75" in the designation means. All values below are the standard AISC published section properties used in US structural design, with metric equivalents alongside. Channel flanges are tapered, so the flange thickness listed is the AISC average value.
Typical uses: stair stringers, trailer and equipment frames, rails, lintels, and bracing — anywhere a flat back against a wall or web is handy. For a quick stiffness check, see the deflection example below or open the beam calculator with your own span and load.
Dimensions
| Depth d | 8 in (203.2 mm) |
| Flange width bf | 2.53 in (64.3 mm) |
| Web thickness tw | 0.487 in (12.4 mm) |
| Avg. flange thickness tf | 0.39 in (9.9 mm) |
Weight & Cross-Section
| Weight per foot | 18.75 lb/ft (27.9 kg/m) |
| 20 ft bar | 375 lb |
| 40 ft bar | 750 lb |
| Area A | 5.51 in² (35.5 cm²) |
Section Properties (strong / weak axis)
| Moment of inertia Ix | 43.9 in⁴ (1,827 cm⁴) |
| Section modulus Sx | 11 in³ (180 cm³) |
| Radius of gyration rx | 2.82 in |
| Moment of inertia Iy | 1.97 in⁴ (82 cm⁴) |
| Section modulus Sy | 1.01 in³ (17 cm³) |
| Radius of gyration ry | 0.6 in |
Compared with the neighbouring sizes
| Shape | d × bf (in) | lb/ft | Ix (in⁴) | Sx (in³) | Δ weight | Δ Ix |
|---|---|---|---|---|---|---|
| C8x13.75 | 8 × 2.34 | 13.75 | 36.1 | 9.02 | −27 % | −18 % |
| C8x18.75 (this page) | 8 × 2.53 | 18.75 | 43.9 | 11 | — | — |
Deflection example
A simply supported C8x18.75 spanning 13 ft with a 10 kip point load at midspan deflects 0.62 in (E = 29,000 ksi, Ix = 43.9 in⁴). The L/360 serviceability limit for this span is 0.43 in — the shape does NOT pass this quick check.
Calculate with your own span and load →
Frequently asked questions
How much does a C8x18.75 channel weigh?
C8x18.75 weighs 18.75 pounds per foot (27.9 kg/m). The number after the "x" in the designation is always the weight in lb/ft. A 20 ft bar weighs 375 lb and a 40 ft bar 750 lb.
What are the dimensions of a C8x18.75?
C8x18.75 is exactly 8 in (203.2 mm) deep with a 2.53 in (64.3 mm) wide flange. The web is 0.49 in thick; the tapered flanges average 0.39 in. Unlike W-shapes, C-channel depths are exact — a C10 is always 10.00 in deep.
What are the dimensions of a C8x18.75 in mm?
C8x18.75 is 203.2 mm deep with a 64.3 mm wide flange; the web is 12.4 mm and the flange 9.9 mm thick. In metric section properties: Ix = 1,827 cm⁴, Sx = 180 cm³.
How much does a C8x18.75 weigh in kg?
27.9 kg per meter. A 6 m bar weighs 167 kg and a 12 m bar 335 kg — handy when ordering US shapes from metric suppliers.
What is the moment of inertia of a C8x18.75?
About the strong axis, Ix = 43.9 in⁴ (1,827 cm⁴) with section modulus Sx = 11 in³. About the weak axis, Iy = 1.97 in⁴ and Sy = 1.01 in³. Use the beam deflection calculator to turn these into deflection and stress for your span and load.
C8x18.75 or C8x13.75 — what does one size down change?
C8x13.75 is about 27% lighter (13.75 vs 18.75 lb/ft) but about 18% less stiff (Ix 36.1 vs 43.9 in⁴). Check deflection before downsizing — stiffness falls much faster than weight.
Values are entered from the governing standard’s published tables and cross-checked programmatically against its mass and section formulas before publication. Spotted an error? Write to advertising@metalabout.net — verified corrections ship within days. About