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.