Electronics calculator
What Ring Light Size Do I Need?
Calculate ring light diameter using subject width, light-to-subject distance, and desired apparent light diameter.
Enter your measurements
Use this recommended-size calculation when you need to answer “what ring light size do i need?” Enter subject width, light-to-subject distance, and desired apparent light diameter and the tool returns ring light diameter using the rule defined for this exact use case.
- Subject width — Required
- Light-to-subject distance — Required
- Desired apparent light diameter — Required
Ring light diameter
Enter the measurements above to calculate ring light diameter.
How the calculation works
V12 calculation: lightDiameter=2×lightDistance×tan(toRadians(desiredAngularDiameter)/2); coverageRatio=lightDiameter/subjectWidth. Angle inputs are explicitly converted to radians before trigonometric functions where required.
Worked example
Example: Subject width = 60 cm; Light-to-subject distance = 250 cm; Desired apparent light diameter = 20 °. Result: Coverage Ratio = 146.94%; Light Diameter = 88.16 cm.
Before you decide
Enter the dimensions that will exist in real use, not an approximate catalogue category. This page calculates the stated geometry or quantity only; product-specific construction or installation details can still affect the final choice. For what ring light size do i need, the limiting result on this page is ring light diameter.
Direct measurement/geometry calculation. No external reference is required for the arithmetic itself; the result is derived only from the user-entered measurements and the formula stored in calculationLogicJson.
Frequently asked questions
What does the Ring Light Size calculator tell me?
It returns ring light diameter from the measurements entered on this page. The calculation is specific to ring light size, so the result should be compared with the exact product or specification you are considering.
Which measurements should I take for ring light size?
Measure subject width, light-to-subject distance, desired apparent light diameter. Use clear, usable dimensions rather than nominal room or product labels.
Should I round the ring light diameter?
Keep the calculated value for comparison, then choose a real product that meets or stays within the returned ring light diameter while allowing for the clearances, tolerances or ratings shown by its manufacturer.