C12x20.7 — Dimensions, Weight & Section Properties
American Standard (C) channel per ASTM A6 / AISC Steel Construction Manual
C12x20.7 is an American Standard steel channel 12 inches (304.8 mm) deep with a 2.94 in (74.7 mm) flange, weighing 20.7 pounds per foot (30.8 kg/m) — that is what the "20.7" 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 | 12 in (304.8 mm) |
| Flange width bf | 2.94 in (74.7 mm) |
| Web thickness tw | 0.282 in (7.2 mm) |
| Avg. flange thickness tf | 0.501 in (12.7 mm) |
Weight & Cross-Section
| Weight per foot | 20.7 lb/ft (30.8 kg/m) |
| 20 ft bar | 414 lb |
| 40 ft bar | 828 lb |
| Area A | 6.08 in² (39.2 cm²) |
Section Properties (strong / weak axis)
| Moment of inertia Ix | 129 in⁴ (5,369 cm⁴) |
| Section modulus Sx | 21.5 in³ (352 cm³) |
| Radius of gyration rx | 4.61 in |
| Moment of inertia Iy | 3.86 in⁴ (161 cm⁴) |
| Section modulus Sy | 1.72 in³ (28 cm³) |
| Radius of gyration ry | 0.8 in |
Compared with the neighbouring sizes
| Shape | d × bf (in) | lb/ft | Ix (in⁴) | Sx (in³) | Δ weight | Δ Ix |
|---|---|---|---|---|---|---|
| C12x20.7 (this page) | 12 × 2.94 | 20.7 | 129 | 21.5 | — | — |
| C12x25 | 12 × 3.05 | 25 | 144 | 24 | +21 % | +12 % |
Deflection example
A simply supported C12x20.7 spanning 19 ft with a 10 kip point load at midspan deflects 0.66 in (E = 29,000 ksi, Ix = 129 in⁴). The L/360 serviceability limit for this span is 0.63 in — the shape does NOT pass this quick check.
Calculate with your own span and load →
Frequently asked questions
How much does a C12x20.7 channel weigh?
C12x20.7 weighs 20.7 pounds per foot (30.8 kg/m). The number after the "x" in the designation is always the weight in lb/ft. A 20 ft bar weighs 414 lb and a 40 ft bar 828 lb.
What are the dimensions of a C12x20.7?
C12x20.7 is exactly 12 in (304.8 mm) deep with a 2.94 in (74.7 mm) wide flange. The web is 0.28 in thick; the tapered flanges average 0.5 in. Unlike W-shapes, C-channel depths are exact — a C10 is always 10.00 in deep.
What are the dimensions of a C12x20.7 in mm?
C12x20.7 is 304.8 mm deep with a 74.7 mm wide flange; the web is 7.2 mm and the flange 12.7 mm thick. In metric section properties: Ix = 5,369 cm⁴, Sx = 352 cm³.
How much does a C12x20.7 weigh in kg?
30.8 kg per meter. A 6 m bar weighs 185 kg and a 12 m bar 370 kg — handy when ordering US shapes from metric suppliers.
What is the moment of inertia of a C12x20.7?
About the strong axis, Ix = 129 in⁴ (5,369 cm⁴) with section modulus Sx = 21.5 in³. About the weak axis, Iy = 3.86 in⁴ and Sy = 1.72 in³. Use the beam deflection calculator to turn these into deflection and stress for your span and load.
C12x20.7 or C12x25 — what does one size up change?
C12x25 is about 21% heavier (25 vs 20.7 lb/ft) but about 12% stiffer (Ix 144 vs 129 in⁴). Going one step up within the same depth group is usually the cheapest way to cut deflection.
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