How can wire length be estimated from a coil?

Approximate the average winding circumference and multiply it by the number of turns and radial layers, adjusted by a packing factor.

Is coil geometry an exact cable-length measurement?

No. Actual winding tension, wire diameter tolerance, packing, spool shape and winding pattern can change the result.

Why does wire diameter matter twice?

Wire diameter determines both approximate turns across the coil width and the number of radial winding layers.

Wound-wire estimation

Wire Coil Length Calculator

Estimate wound wire length from coil dimensions while making the geometric assumptions visible instead of treating a rough coil measurement as exact inventory.

Coil geometry

Outer coil diameter

Inner coil / former diameter

Coil winding width

Wire diameter

Packing factor (%)Compensates for imperfect geometric packing.

Number of identical coils

Dimension unit

This is a geometric estimate. Actual wound length can differ because of wire diameter tolerance, winding pattern, tension, voids and spool construction.

Enter the coil diameters, width and wire diameter.

Estimated wire length

Wire per coil

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—Turns / layer

—Radial layers

—Average circumference

—Total wire

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Coil-length method

The calculator estimates the number of turns across the coil width and the number of radial layers between the former and outer coil diameter. It uses the average coil diameter for an average winding circumference, then applies the packing factor.

Turns per layer ≈ coil width ÷ wire diameter
Radial layers ≈ (outer diameter − inner diameter) ÷ (2 × wire diameter)
Average circumference = π × (outer diameter + inner diameter) ÷ 2
Length ≈ circumference × turns × layers × packing factor

Worked example

For a 300 mm outer diameter, 100 mm inner diameter, 200 mm width and 2 mm wire, the nominal model gives about 100 turns per layer and 50 radial layers. A 92% packing factor reduces the geometric estimate accordingly.

Why use a packing factor?

Real winding is not a perfectly dense mathematical lattice. The packing factor gives you an explicit way to account for practical voids without pretending the adjustment is a universal constant.

Frequently Asked Questions

Can the inner diameter be zero?

No useful spool-based model exists without an inner radius, so the calculator requires a positive former diameter.

Can the packing factor be 100%?

Yes mathematically, although it represents the idealized geometric case rather than a guaranteed physical winding result.