Engineering Tools
Watt Density Calculator
Check surface watt density of cartridge and tubular heaters.
Surface watt density
13.55W/cm²
In imperial
87.4W/in²
Heated surface
36.9cm²
Typical maximum watt density (guidance)
- Still air≤ 3 W/cm² ✗
- Forced air (duct)≤ 6 W/cm² ✗
- Heavy / heat-transfer oil≤ 3.5 W/cm² ✗
- Light oil≤ 5 W/cm² ✗
- Water≤ 9 W/cm² ✗
- Cartridge in tight-fit metal bore≤ 25 W/cm² ✓
How it works
Watt density is the heater's power divided by its heated surface area. It is the single most important number for heater life: too high for the medium and the sheath overheats, oil cokes, or the element burns out early.
For a cylindrical heater the heated surface is π × diameter × heated length, where heated length is the overall length minus the unheated (cold) zones at the ends.
Results are engineering estimates for initial sizing. Final heater design should be confirmed with our application engineers.