Sheet Metal Cone Flat Pattern Calculator

Inputs

Large diameter (D1)

Large finished diameter of the frustum.

Small diameter (D2)

Small finished diameter. Use 0 for a full cone.

Vertical height (H)

Straight vertical height, not slant height.

Seam allowance

Straight seam allowance added as a simple slant-height strip for area estimating.

Default result

Pattern sector angle(theta)

103.45°

Pass

Also computed

Outer pattern radius(R1)530.37mm

Inner pattern radius(R2)265.18mm

Slant height(s)265.18mm

Large arc length957.56mm

Small arc length478.78mm

Pattern area190,450mm²

Method notes 3 notes

Slant height s = sqrt(H^2 + ((D1 - D2)/2)^2). Pattern radii are s*D1/(D1-D2) and s*D2/(D1-D2).
Sector angle comes from matching the developed outer arc to the finished large circumference: theta = 180*D1/R1 degrees.
This is a geometric flat-pattern screen. Thickness compensation, bend/stretch allowance, forming method, locks, hems, notch relief, grain direction and shop tooling are not included.