Film developing calculators
Calculators and data-sheet tables for the sums that come before every roll you develop at home: how much longer the next roll needs in a developer you reuse (Cs41 and ID-11), how long to develop when the water isn't at 20 °C, and how much concentrate goes in the tank. Each page names the data sheet behind its numbers and links to it, so you can check them against the instructions that came with your chemistry.
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Cs41 and developer reuse time calculator
For developers you pour back into the bottle, like ID-11 stock or a C-41 kit. Enter the maker's rule (add a percentage per roll, up to a set number of rolls) and get the time for the roll you're about to develop, plus how many rolls the developer has left.
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HC-110 and film developer dilution calculator
Enter a dilution like 1+31 or 1:50 and your tank volume. You get mL of concentrate and mL of water, and a check against the minimum amount of concentrate per roll where the maker states one (Adox does for Rodinal).
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Film developing temperature compensation calculator
Enter the time your data sheet gives at 20 °C and the temperature of your developer. You get the adjusted time from a curve fitted to Ilford's time/temperature chart, with a warning outside the chart's 18–27 °C range.
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How many rolls per CineStill Cs41 kit
Up to 24 rolls per quart on CineStill's product page, 8 in the instructions. A table gives the developer time for every roll at +2% each.
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Ilfosol 3 development times
Ilford's times for HP5 Plus, FP4 Plus, T-Max and Tri-X at 1+9 and 1+14, at 20 and 24 °C, with agitation and tank volumes.
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D-76 development times
Kodak's times for stock and 1:1 for Tri-X, T-Max, Plus-X and Verichrome at 20 °C, with agitation, capacity and replenishment.
A worked example
Kodak's HC-110 data sheet (J-24) lists dilution B as 1:31 from concentrate. In a 500 mL tank that is 1 part concentrate in 32 parts of solution, so 15.6 mL of concentrate and 484.4 mL of water. Kodak's own table rounds it to 16 mL. The dilution calculator does this sum for any ratio and tank.
Temperature works the same way. Ilford's Ilfosol 3 sheet says to take 10% off the time for each degree above 20 °C, so a 4-minute development becomes about 3 minutes at 23 °C (the sheet's own example). The temperature calculator handles other times and temperatures, in °C or °F.
Developers and films covered
The dilution calculator takes any ratio. Its quick picks are HC-110 dilutions B and E, Rodinal (Adonal) at 1+25, 1+50 and 1+100, ID-11 at 1+1 and Ilfosol 3 at 1+9 and 1+14. Rodinal's minimum of 5 mL of concentrate per roll comes from Adox via Fotoimpex, and the tank volumes from a Paterson retailer listing and Adox's Jobo figures.
The temperature calculator follows Ilford's time/temperature chart between 18 and 27 °C and warns outside it. The reuse calculator holds Ilford's rules for ID-11, Microphen and Perceptol stock and CineStill's Cs41 instructions. Ilfosol 3 times for HP5 Plus, FP4 Plus, T-Max and Tri-X are on their own page.
Color is covered for Cs41 only. Other C-41 kits come with their own tables, and the reuse calculator accepts their rule if you type it in.
Where the numbers come from
Most figures come from manufacturer sheets I opened, and each page names and links its source. The temperature curve is my own fit to Ilford's chart, and the page says so. When two sources disagree, as Cs41's product page and instructions do on rolls per kit, the page says so and shows both. Your own data sheet still has the last word, and a developing time is a starting point you adjust to your negatives.
Nothing you enter is stored.
What's next
I'm planning a roll log: one line per roll with the film, developer, dilution, time, temperature and a note on how the negatives came out, so you can see which recipe gave the best results on a given film. It isn't built yet, and these calculators don't save anything you enter. A saved log may come later, and the calculators stay free.
If one of these calculators helped or got something wrong, the buttons at the bottom of the page tell me.