Film Speed Converter
Convert between ISO, ASA, and DIN film speed ratings. ISO and ASA are arithmetically equivalent, while DIN uses a logarithmic scale where each 3° increase doubles the sensitivity.
Convert film speed
Enter a value in either ISO/ASA or DIN
Common speeds
ISO
100
ASA
100
DIN
21°
Quick reference
| ISO/ASA | DIN | Typical use |
|---|---|---|
| 25-50 | 15°-18° | Fine grain, bright light, studio |
| 100-200 | 21°-24° | General purpose, daylight |
| 400 | 27° | Versatile, indoor/outdoor |
| 800-1600 | 30°-33° | Low light, action, indoor |
| 3200+ | 36°+ | Very low light, pushed film |
About film speed scales
ISO / ASA
The arithmetic scale where doubling the number doubles the sensitivity. ISO 400 is twice as sensitive as ISO 200. The ISO standard (from 1974) adopted the American ASA scale, so they are interchangeable.
DIN
The German logarithmic scale where adding 3° doubles the sensitivity. DIN 24° is twice as sensitive as DIN 21°. Written with a degree symbol (°).
Conversion formula
DIN = 10 × log₁₀(ISO) + 1
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