Cable Sizing Calculator Formula
Understand the math behind the cable sizing calculator. Each variable explained with a worked example.
Formulas Used
Minimum Conductor Area
min_area = current / max_current_densityVariables
| Variable | Description | Default |
|---|---|---|
current | Design Current (I)(A) | 40 |
max_current_density | Max Current Density(A/mm^2) | 4 |
How It Works
Cable Sizing by Current Density
The cable must carry the required current without exceeding safe temperature limits.
Simplified Method
A = I / J
where A is the conductor cross-sectional area, I is the design current, and J is the allowable current density. Typical values: enclosed cables 3-4 A/mm^2, open-air cables 5-6 A/mm^2. Always verify against manufacturer ampacity tables and installation derating factors.
Worked Example
40 A load with 4 A/mm^2 allowable current density.
current = 40max_current_density = 4
- 01A = 40 / 4 = 10 mm^2
- 02Select the next standard size: 10 mm^2 or 16 mm^2 depending on available sizes.
- 03Also verify voltage drop is within limits for the cable run length.
Ready to run the numbers?
Open Cable Sizing Calculator