How to use the luminance converter
- Type the brightness in Value, for example 14.
- Choose its unit in From, such as foot-lamberts.
- Choose the unit you want in To, such as cd/m² (nit).
- Read the result and the full table of eight units. Use the swap button to convert the other way.
What it does and when to use it
Luminance is the brightness of a surface you look at: a phone screen, a projection screen, a lit sign or a sheet of paper on a desk. Different trades still use different units for it. Display makers quote nits, cinema and projection work often uses foot-lamberts, lighting engineers may quote cd/ft² or kcd/m², and older European texts use the stilb, lambert and apostilb.
Typical jobs are comparing a projector rated in foot-lamberts with a TV rated in nits, checking a display’s peak brightness against a calibration target, or reading a lighting standard written in a different unit. To set the colour of the light rather than its brightness, use the mired and colour temperature converter.
How it works
Each unit is stored as a number of candelas per square metre. The result is value × from-factor ÷ to-factor.
| Unit | cd/m² |
|---|---|
| kcd/m² | 1,000 |
| stilb (cd/cm²) | 10,000 |
| cd/ft² | 1 ÷ 0.3048² ≈ 10.7639 |
| cd/in² | 1 ÷ 0.0254² ≈ 1,550.003 |
| foot-lambert | 1 ÷ (π × 0.3048²) ≈ 3.42626 |
| lambert | 10,000 ÷ π ≈ 3,183.099 |
| apostilb | 1 ÷ π ≈ 0.318310 |
The foot and inch are exact (0.3048 m and 0.0254 m), and π is used at full double precision, so the only rounding is in the display.
Worked examples
Cinema screen. 14 fL = 47.9676273949 cd/m² (nit). Digital cinema guidance is commonly quoted as 14 fL or 48 cd/m², and this shows why those two figures go together.
Bright monitor. A display that reaches 1,000 nits is 291.86350796 foot-lamberts.
An old unit. 1 lambert = 3,183.09886184 cd/m² (nit), which is 10,000 ÷ π.
Limits and tips
- Luminance is directional. A screen’s nits are usually measured straight on; viewing from the side often gives a lower reading. The converter cannot correct for that.
- HDR peak figures often apply to a small patch of the screen for a short time, so a full-screen value can be much lower.
- Tiny values below 1e-9 appear in scientific notation in the table.
- For screen sharpness rather than brightness, the PPI calculator works out pixel density.
Frequently asked questions
What is a nit?
How many nits is one foot-lambert?
Is luminance the same as lux or lumens?
Why do some units contain π?
Can I convert a monitor's nits into its lumens?
Sources
- NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically — NIST, accessed 2026-10-08
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