Darkroom tools

Mix Temperature

Got some of the solution already measured out? Find out how warm the rest of the water has to be to hit the working temperature.

Working solution

What you already have

Developer concentrate, stock solution, water already in the jug…

    Top up with

    – of water at
    –
    Split between two sources

    Hot and cold tap, kettle and fridge… measure each one just before pouring.

    – hot + – cold

    How it works

    Mixing water is a weighted average: every part brings its volume times its temperature. The calculator balances the total, treating every part as water — close enough for diluted developers.

    Switch a part to 1+n to enter it as a dilution: 1+9 is one part concentrate to nine parts water, so 37.5 ml in a 375 ml solution. Datasheets that write 1:9 usually mean the same.

    Split between two sources works out how much hot and cold water make up the top-up, so you can measure both straight into the graduate instead of fiddling with the tap.

    Jugs, tanks and the reels soak up some heat. If the mix keeps coming out a touch cold, aim half a degree warmer.