Nichrome Wire Calculator (Heating Element Length)
Length of nichrome wire for a heating element of a given voltage and power, with the resistance, the current and the power per area of wire surface.
Results
The dashed line marks the value you entered.
What this tool does
A heating element must have a resistance of V² ÷ P, and the length of wire that gives it follows from the wire's resistivity and cross-section: nichrome 80/20 is about 1.10 µΩ·m, and a thin wire has far more resistance per metre than a thick one. Resistivity changes a little with temperature, so the hot wire differs somewhat from the cold figure. The surface loading — watts per square centimetre of wire surface — is the number that decides life: the more power per area, the hotter and shorter-lived the wire, and the safe value depends on whether it sits in still air, moving air or water. Powered from mains it is a shock and fire hazard, so build it into an enclosure.
Formula
R = V² ÷ P · A = π d² ÷ 4 · length = R × A ÷ ρ (nichrome 80/20: ρ ≈ 1.10 µΩ·m at 20 °C)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
v | Voltage | V |
p | Power | W |
d | Diameter | mm |
ro | Resistivity of the wire | µΩ·m |
LN | Length of wire needed | m |
R | Resistance the element must have | Ω |
I | Current | A |
RM | Resistance per metre of wire | Ω/m |
SL | Surface loading (power per area of wire surface) | W/cm² |
Worked example
- Voltage12 V
- Power60 W
- Diameter0.5 mm
- Resistivity of the wire1.1 µΩ·m
- Length of wire needed0.43 m
- Resistance the element must have2.40 Ω
- Current5.00 A
- Resistance per metre of wire5.60 Ω/m
- Surface loading (power per area of wire surface)8.9 W/cm²
Limitations
- Electrical installations are governed by national wiring rules. Cable sizing also depends on installation method, grouping, ambient temperature and protection devices, which this calculator does not evaluate.
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.