Induction Heater Work Coil Calculator

This simple calculator will estimate the inductance of a flat pancake coil used in induction heaters, based on:

• Number of turns (N)
• Spacing between turns (s) in millimeters
• Wire diameter (optional, we’ll assume it’s negligible unless you want it)
• Coil outer and inner diameter (to get average radius)

Formula to Estimate Inductance (Pancake Coil)

We’ll use an approximate formula derived from the Wheeler formula for spiral coils:

L = (μ₀ * N² * r²) / (8r + 11w)
Where:

L is inductance in Henries

μ₀ = 4π × 10⁻⁷ H/m (permeability of free space)

N = number of turns

r = average radius of the coil in meters

w = radial width of the coil (outer radius - inner radius) in meters

We can calculate:

w = (N - 1) * spacing

r = (inner_diameter + outer_diameter) / 4