Power Density Calculator — W/cm²

Methodology

The power density is the key parameter that determines the surface temperature of a cartridge heater during operation and therefore its service life. It is expressed in watts per square centimetre (W/cm²) and is calculated by dividing the rated power by the active heating surface area.

Formula

W/cm² = P / S

• P — Rated power of the cartridge heater (W)
• S — Active heating surface area (cm²) = π × D × L_active

D is the outer diameter in cm and L_active is the heated length in cm (total length minus cold zone).

Power density ranges

• High density: up to 25 W/cm² — plastic injection, extrusion, precision tooling
• Medium density: 10–18 W/cm² — industrial mould and die heating
• Low density: up to 10 W/cm² — controlled-temperature processes, longer service life

Worked example

Cartridge heater rated 300 W, diameter 12.7 mm, heated length 150 mm:

1. Active surface area: S = π × 1.27 cm × 15 cm = 59.85 cm²
2. Power density: 300 W / 59.85 cm² = 5.01 W/cm²

Result: low density. Suitable for long-service-life applications in materials with limited thermal contact.

High power density without sufficient contact between the heater and the bore causes overheating of the heating wire and dramatically shortens service life. The recommended diameter fit is H7/h6.