How do I draw accurate arches for building models?

Calculate the width and rise, then use a compass or flexible curve. For Gothic arches, the radius equals the width. For semicircular arches, the radius is half the width. Draw on card first as a template, then trace onto your building material.

How do I cut accurate circles in styrene?

For small circles, use a circle cutter or compass with a sharp blade. For larger circles, drill a pin hole at centre and rotate the sheet against a fixed blade. Templates cut from card can be traced onto sheet and cut with repeated light passes.

What is a compound curve?

A compound curve changes radius along its length — like the bow of a ship or the leading edge of a wing. These are best created by plotting multiple points from reference drawings and connecting them with a flexible spline or French curve.

How do I transfer templates to sheet material?

Draw or print the template on paper/card. Cut it out carefully. Tape or hold it against your sheet material and trace around it with a fine scriber or sharp pencil. For repeated parts, make a master template from thick card or thin ply.

ModelCalcs

Template Calculator — Shapes & Curves

Generate dimensions for templates including circles, arches, angles and compound curves.

Shape

Diameter (mm)

How We Calculate This

Calculates geometric properties for common template shapes used in scratch-building.

Formulas

Circle: Perimeter = Pi x Diameter, Area = Pi x r squared
Arch: Arc length = Pi x sqrt((w/2)^2 + h^2) / 2)
Arc: Arc length = Radius x Angle (radians)
Chord = 2 x Radius x sin(Angle / 2)

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify quantities before purchasing materials.