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.

ShapeCircle for portholes/wheels, Arch for door & window heads, Arc for curved roof/canopy sections, Angle for gussets and bracing

Diameter (mm)

How We Calculate This

Calculates geometric properties for common template shapes used in scratch-building — so you can mark out card masters and cut sheet styrene to size.

Formulas

Circle: Perimeter = π × Diameter; Area = π × r²
Arch (half-ellipse): Arc length = π × √(((w÷2)² + h²) ÷ 2) — exact for a semicircle (rise = half-width)
Arc: Arc length = Radius × Angle (in radians); Sector area = ½ × r² × Angle
Angle (two equal sides): Open end (chord) = 2 × side × sin(Angle ÷ 2); Area = ½ × side² × sin(Angle); Perimeter = 2 × side + chord

Frequently Asked Questions

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Last updated: February 2026

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