WINDING SPACE · WIRE · RESISTANCE
Bobbin Winding Calculator
Turn a winding window into a practical starting specification. Enter the bobbin surface dimensions and finished wire diameter, then check fit, layer arrangement and copper requirements.
Check your winding layout
Results update as you editFROM INPUT TO SPECIFICATION
How to use this calculator
Start with a known design requirement, check the assumptions, and keep a record of the values you used.
Define the winding space
Enter the bobbin outside dimensions, inner corner radius, available traverse and radial allowance. Reserve space for side margins and any layer insulation.
Choose wire and turn count
Use the supplier’s finished wire diameter for packing. Enter turns to check a design, or calculate the turn capacity of the available space.
Review fit and save the design
Inspect the layer arrangement, required dimensions, copper weight and resistance. Export the calculation and share it with your drawing for a manufacturing review.
METHOD & SCOPE
What the calculation means.
Geometry first. Copper calculations second.
The model places wire across the usable traverse, one radial layer at a time. Aligned and ideal staggered packing are available; a final partial layer still contributes to maximum radial build.
Wire length sums the centerline perimeter of every turn, then adds two equal leads. Copper area uses the bare diameter. The reference resistivity is 0.017241 Ω·mm²/m at 20 °C and copper density is 8.96 g/cm³.
Use the winding boundary for the R corner
For a rectangular bobbin, enter the corner radius at the inner winding boundary. Each layer’s centerline radius increases with its distance from that boundary. The tool does not treat this input as a finished outer corner radius.
Fit is an ideal geometric estimate. Crossovers, wire stretch, winding tension and manufacturing slack are not included. Interlayer tape is treated as a flat separator. Inductance and magnetic performance require a separate model.
DESIGN QUESTIONS
Before you build.
Should I enter bare wire diameter or finished wire diameter?
Enter both. The bare copper diameter determines copper area, resistance and copper weight. The finished diameter includes enamel or other insulation and determines how many wires fit across the winding space. An AWG value only supplies a nominal bare diameter.
Which dimensions define a rectangular bobbin?
Use the outside dimensions of the bobbin surface directly underneath the wire, together with its corner radius. These form the inner boundary of the winding. They are different from the bobbin bore and the finished coil outside dimensions.
Does copper weight include the leads?
Yes. The calculation adds two leads of the entered length, using the same copper diameter as the winding. The initial setting is 60 mm per lead, or 120 mm total. Copper weight excludes enamel, bobbin, tape and terminals.
Does a fit result guarantee that the coil can be manufactured?
No. The layout is an ideal geometric estimate. Manufacturing review must consider actual wire tolerances, winding tension, crossovers, process allowances, insulation and termination details. This tool does not calculate inductance or certify a winding.
CONTINUE YOUR DESIGN
The next step for your coil.
Keep the calculation with your drawing and target specifications when discussing a coil design.