Film & darkroom
How to calculate film developer dilution
A worked example of 1+4, with total volume kept separate from concentrate.
The dilution notation is part of the recipe. Read it exactly as the manufacturer defines it. In the 1+4 convention used here, one part concentrate is mixed with four parts water, making five parts of working solution.
A 300 ml example
For a documented 1+4 working dilution and a chosen total of 300 ml, divide 300 by five: 60 ml concentrate plus 240 ml water. Our arithmetic gives the final volume, but the product sheet must establish that the dilution is appropriate and the tank must establish that the volume covers the loaded film.
Evidence: Manufacturer guidance
Choose the measuring vessel
Write the required total beside your tank configuration before calculating. Use a vessel whose graduations let you measure the smaller concentrate amount clearly. Check both numbers aloud against the sheet before mixing, and keep each chemical’s measuring equipment identified. Do not treat a partly filled tank as a way to economise on developer.
Different notation needs a definition
Stock solution, working solution and concentrate are separate terms. A powder may first become stock and then be diluted again for use. Our worksheet therefore has two boxes: preparing the stock, and preparing the working bath. Never substitute a dilution taken from another product merely because its bottle looks similar.
Sources & further reading
Sources for the specific facts and product descriptions above. Our worked examples, interpretations and practical suggestions are original editorial guidance.
- ILFORD PHOTO — choosing chemicals for processing filmManufacturer guidance