Concentrate needed
0 ml
Water needed
0 ml
Rolls per bottle (500ml concentrate)
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Mix the right amount of concentrate and water for your tank volume and dilution ratio. Works with any dilution from 1+9 to 1+100.
Film developers are sold as liquid or powder concentrates. You dilute them with water to make working solution, which is what you actually use in the tank. A dilution ratio like 1+31 means one part concentrate plus 31 parts water, for 32 parts total. If your tank needs 300ml and you choose 1+31 dilution, you calculate: 300 divided by 32 = 9.4ml concentrate plus 290.6ml water.
Tank volume is essential. The amount of working solution you mix depends entirely on your tank and film format. A single 35mm roll needs about 300ml, a single 120 roll needs 500ml. Check your tank bottom for the exact volumes engraved there. Using too little developer leaves part of the film uncovered and underdeveloped. Using more than the minimum is fine.
Weaker dilutions need more concentrate. A 1+50 dilution is less active than 1+25, so you can keep the film in the developer longer for more consistent results. But weaker dilutions require more concentrate to stay above the minimum. If your developer has a 50ml minimum and you are making 500ml at 1+50 dilution, you need 500 divided by 51 = 9.8ml concentrate. That is well above the 50ml minimum, so it works. But at 1+100, you only need 500 divided by 101 = 4.9ml concentrate, which falls far short and may cause uneven development.
The minimum concentrate matters. Most developers (Ilford, Kodak, Agfa) specify a minimum amount of full-strength concentrate per roll, usually 50ml to 100ml. This is not a ratio, it is an absolute quantity. Dilute below this minimum and the developer may be exhausted before the film is fully developed, or development becomes uneven across the roll. The calculator above warns when your setup falls short. Check your developer's data sheet for the exact minimum recommended for your brand.
Use these volumes as your starting point. Always verify against the bottom of your specific tank, as sizes vary slightly by manufacturer and model.
| Film format | Reels | Volume (ml) |
|---|---|---|
| 35mm | 1 | 290-300 |
| 35mm | 2 | 600 |
| 120 roll | 1 | 500 |
| 120 roll | 2 | 1000 |
| 220 roll | 1 | 600-800 |
| 110 or 126 | 1 | 200 |
These are typical volumes for universal tanks like Paterson models. Some manufacturers vary slightly. You can fill with slightly more solution than the minimum without problems, which is often recommended to ensure the reel stays submerged throughout development and agitation.
| Ratio | Concentrate factor | Typical use |
|---|---|---|
| 1+9 | Stock strength | Fine-grain, controlled contrast. Shortest times. |
| 1+25 | Full strength | General purpose. Good grain and contrast. |
| 1+31 | Near normal | Slightly less active than 1+25. Longer times for finer grain. |
| 1+50 | Half strength | Dilute and compensating. Long development times for even results. |
| 1+100 | Very dilute | Extreme dilution and compensating. Needs high minimum concentrate. |
Weaker dilutions (higher numbers after the plus sign) produce finer grain but require longer development times. They also require more total concentrate to stay above the minimum per-roll requirement. Most photographers work with 1+25 to 1+50 for practical consistency.
Developer temperature affects how fast development proceeds. Higher temperature speeds it up, lower temperature slows it down. Most development times are given for 20°C (68°F). To adjust for a different temperature, use this formula:
Adjusted Time = Base Time × 1.04 ^ (20 - actual temperature)
For example, if your base time at 20°C is 10 minutes and your developer is at 24°C:
Adjusted Time = 10 × 1.04 ^ (20 - 24) = 10 × 1.04 ^ (-4) = 10 × 0.854 = 8.5 minutes
A few worked examples:
| Actual temp | Multiplier | Example (base 10 min) |
|---|---|---|
| 18°C | 1.082 | 10.8 minutes |
| 20°C | 1.000 | 10.0 minutes |
| 22°C | 0.924 | 9.2 minutes |
| 24°C | 0.854 | 8.5 minutes |
| 25°C | 0.821 | 8.2 minutes |
Temperatures below 16°C or above 26°C produce increasingly unpredictable results. Most developers work best between 18°C and 24°C. If you do not have a thermometer, develop in a room at a stable temperature and run the same temperature each time for repeatable results.
A single 35mm roll requires about 300ml of working strength developer. The concentrate amount depends on your dilution ratio. For a 1+31 dilution with 300ml total volume, you need 300 divided by 32, which is about 9.4ml of concentrate and 290.6ml of water.
A 1+25 dilution means 1 part developer concentrate to 25 parts water, for 26 parts total. If your tank needs 300ml, the concentrate share is 300 divided by 26, which is about 11.5ml of concentrate and 288.5ml of water.
Yes. If you use too little concentrate, development can fail or become uneven, ruining the film. Most developers require a minimum of 50ml to 100ml of full-strength concentrate per roll, regardless of dilution ratio. The calculator warns you when this minimum is at risk.
A single 120 roll requires 500ml of working developer in a Paterson-style universal tank. Two 120 rolls require 1000ml. Always check the bottom of your specific tank for the exact volume engraved on it, as some tanks vary.
Use the formula: Adjusted Time = Base Time × 1.04^(20 - actual temperature in Celsius). For example, if your base time at 20°C is 10 minutes and the developer is at 24°C, the adjusted time is 10 × 1.04^(20-24) = 8.5 minutes. Higher temperature means shorter development time.
Tank volume affects how much working solution you mix. Too little developer and the film will not be fully covered during development. Manufacturers specify the minimum volume for each film format and reel count. Mixing more than the minimum is fine and is sometimes recommended to ensure the reel stays submerged.