Temple Spread Angle Calculator | Eyewear Fit and Comfort Measurement
Temple Spread Angle Calculator
Evaluate the temple opening angle of your eyewear to achieve a comfortable and stable fit.
Temple Spread Angle Calculator
Enter your frame and head dimensions to estimate the temple spread angle.
Field Descriptions
- Temple Tip Distance: The distance between the ends of both temples when the frame rests on a flat surface.
- Frame Back Width: The inner width of the frame at the back (between the hinge points). Typically 125–140 mm for adults.
- Temple Length: The length of each temple arm, measured from hinge to tip. Standard range: 135–150 mm.
- Temple Spread Angle: The angle formed between the temples when viewed from above, calculated from geometry.
Ideal range: 95°–110°, depending on frame design and material flexibility.
About Temple Spread Angle
The Temple Spread Angle (TSA) is a key geometric measurement that defines the degree of opening between the two temple arms of an eyeglass frame. It determines how tightly or loosely the frame fits around the wearer’s head. This parameter directly affects comfort, grip stability, and the frame’s ability to maintain its position during daily activities.
The TSA is calculated using the temple tip distance, frame back width, and temple length. By modeling each temple as a rigid arm hinged at the frame, the spread angle can be estimated geometrically:
TSA = 2 × arccos((Frame Back Width / 2) / Temple Length)For most adults, an optimal spread angle falls between 95° and 110°. Angles below 95° indicate a tight fit, which may cause excessive temple pressure and discomfort over prolonged wear. Conversely, angles above 110° suggest a loose frame, which can slip easily, especially during movement or perspiration.
Designers and opticians use TSA values during the adjustment and quality-control phase. For metal or acetate frames, a small temple angle ensures a snug fit and prevents the frame from shifting forward. Titanium or flexible polymer frames, however, may allow a wider TSA without compromising comfort due to material elasticity.
The temple spread angle also contributes to the frame’s overall aesthetic balance. A symmetrical TSA enhances visual alignment with facial contours, reducing the “flared” appearance often seen in oversized or poorly adjusted frames. When designing new eyewear collections, engineers may integrate TSA data into digital frame modeling software to simulate ergonomic fit across different head sizes.
In professional optical workshops, TSA adjustments are often performed manually using warm air or infrared heating for acetate frames. Even a 2–3° change can transform the comfort level, making it a critical adjustment parameter during final fitting. When combined with pantoscopic and face form angles, TSA completes the trio of 3D frame geometry that defines true optical alignment.
Understanding and accurately measuring the Temple Spread Angle can help designers optimize frame ergonomics, improve wearer satisfaction, and reduce returns due to poor fit. This makes the TSA not only a design parameter but a cornerstone of professional eyewear fitting.