The Gothic Arch calculator will return the radius for the given arch width and rise.
Types of Gothic Arches Supported.
Equilateral Gothic Arch. An arch whose opening and radius of the two halves form an equilateral triangle.
Lancet Gothic Arch. A two-centered arch with the radius centers located outside the opening and on the spring line.
Drop Gothic Arch. A two-centered arch with the radius centers located inside the opening and on the spring line.

Arch Width
Enter the width of the opening.

Arch Rise
Enter the rise-height of the opening.

Length/Dimensions Input Menu Mode
1. Imperial/English Inch base 12 —— default.. use American standard pitches over 12.
2. Metric 300mm base —— 300mm is 11.81102 inches, similar usage to the American framing squares printed in inches.
3. Decimal Inch base 10 —— use this option when working with tangents or using the Chappell Master Framing Square multiply the tangent of the angle by 10

The output mode selection can be completely different from the input mode.

Length/Dimensions Output Menu Mode
1. Imperial/English Inch base 12 —— default.. use American standard pitches over 12.
2. Metric 300mm base —— 300mm is 11.81102 inches, similar usage to the American framing squares.
3. Decimal Inch base 10 —— use this option when working with tangents or using the Chappell Master Framing Square