Enter the busbar width, the thickness, and an assumed allowable current density (A/mm²) into the calculator to estimate the busbar current.

Busbar Current Calculator

Enter any 3 values to calculate the missing variable (uses I = Area × Current Density; results are an estimate).

Busbar Current Formula

The following relationship can be used to estimate busbar current from cross-sectional area and an assumed allowable current density. Allowable busbar current is not determined by material alone; it depends on allowable temperature rise, ambient temperature, enclosure/ventilation, orientation, spacing to other conductors, duty cycle, and (for AC) skin/proximity effects. For design/compliance, use applicable standards and/or manufacturer ampacity data.

I_{bb}=w\cdot t\cdot J
  • Where Ibb is the estimated busbar current (amps)
  • w is the width (mm) 
  • t is the thickness (mm) 
  • J is the assumed allowable current density (amps/mm²)
    • Copper (common conservative starting point in natural convection): ~1.0–1.6 A/mm²
    • Aluminum (common conservative starting point in natural convection): ~0.6–1.0 A/mm²
    • Enclosed/poor ventilation: use a lower current density (may require values below 1 A/mm² for copper)
    • Forced cooling/short duty: higher current densities may be possible—verify with applicable standards or manufacturer data

To estimate busbar current, multiply the width and thickness to get cross-sectional area, then multiply by the assumed allowable current density.

How to Calculate Busbar Current?

The following example problems outline how to calculate Busbar Current.

Example Problem #1

  1. First, determine the width (mm). In this example, the width is 40 mm.
  2. Next, determine the thickness (mm). For this problem, the thickness is 10 mm.
  3. Next, choose an assumed allowable current density J (amps/mm²). In this example, J is assumed to be 1.2 A/mm² (example value).
    1. Finally, calculate the Busbar Current using the formula above: 

Ibb = w × t × J

Inserting the values from above and solving yields: 

Ibb = 40 × 10 × 1.2 = 480 (amps)

Example Problem #2

Using the same method as above, determine the variables required by the formula. For this example problem, these are:

width (mm) = 5

thickness (mm) = 3

assumed allowable current density J (amps/mm²) = 0.6

Entering these given values into the calculator above yields: 

Ibb = 5 × 3 × 0.6 = 9 (amps)