Gear Measurement

Gear Measurement

Calculate theoretical span measurement and chordal tooth dimensions for a standard external involute spur gear.

Gears & Indexing
Use this to set or inspect tooth thickness with a gear-tooth/span micrometer or chordal gear-tooth caliper. Initial scope is standard, zero-profile-shift external spur gears.

Live Measurement View

See where the selected inspection dimension is taken. Change the span count or select a method below.

Span · 3 teeth

Parallel measuring faces span the selected number of teeth. The displayed W is the theoretical base-tangent/span measurement.

Calculation Rules & Open Sources

Span measurement uses W = m cos α [π(k−0.5) + z·inv(α)], where inv(α)=tan α−α with α in radians. Recommended span count is the nearest integer to z·α/180 + 0.5 for this zero-profile-shift spur-gear scope.

Base geometry is cross-checked against FreeCAD Gear Workbench / documentation and BOSL2. The span relation is implemented from open published derivations and independently regression-tested; no proprietary handbook table is copied.

Engineering reference only. Theoretical values assume standard involute geometry with zero profile shift and zero backlash allowance. Use the drawing's specified inspection method/tolerance for acceptance. Terms & Disclaimer