Analog Film Development Time Calculator
Calculate adjusted darkroom film development time based on temperature and developer dilution.
For black and white film photography.
Analog film development is a chemical process where exposed film is soaked in developer solution to make the latent image visible. Temperature directly affects how fast the chemical reaction occurs — even a 1°C difference can noticeably change results.
The Ilford/Kodak temperature adjustment rule:
For every 1°C above 20°C (68°F), reduce development time by approximately 10%. For every 1°C below 20°C (68°F), increase development time by approximately 10%.
More precisely:
Adjusted Time = Base Time × (0.9 ^ ΔT°C) when warmer
Adjusted Time = Base Time × (1.1 ^ |ΔT°C|) when cooler
A more accurate formula uses the activation energy method:
T₂ = T₁ × (0.26 ^ ((Temp₂ - Temp₁) / 10))
Most photographers use a simplified compensation factor of 10% per 1°C, which is accurate enough in the 18–24°C range.
Common developer times at 20°C (68°F):
| Film | Developer | Dilution | Time at 20°C |
|---|---|---|---|
| Kodak Tri-X 400 | D-76 | Stock | 7.5 min |
| Kodak Tri-X 400 | D-76 | 1+1 | 10 min |
| Kodak T-Max 400 | T-Max Dev | Stock | 7 min |
| Ilford HP5 Plus | ID-11 | Stock | 7.5 min |
| Ilford HP5 Plus | HC-110 | B (1+31) | 6 min |
| Ilford Delta 400 | ID-11 | Stock | 9 min |
| Kodak Tri-X 400 | Rodinal | 1+50 | 12 min |
| Ilford FP4 Plus | ID-11 | Stock | 6 min |
Agitation pattern:
Standard agitation: Invert the tank continuously for the first 60 seconds, then 3–4 inversions every 30 seconds. Less agitation = slightly lower contrast and finer grain. More agitation = higher contrast and potentially more grain.
Temperature stability is critical:
A water bath at your target temperature keeps the developer, stop bath, and fixer all at the same temperature. Fluctuations of more than 1°C during development can cause uneven results.
Stop bath and fixer times are less temperature-sensitive than developer. Typically 1 minute in stop bath and 3–5 minutes in fresh rapid fixer are sufficient across normal temperatures.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.