Darkroom Timer & Calculator

Traditional darkroom printing still involves a lot of small calculations, done in dim light with wet hands. This tool handles the three most common ones, rescaling exposure for a new print size, building f-stop test strips and mixing chemistry, and adds a countdown you can hear, so you do not have to watch a screen.

New print size

When you raise the enlarger head to print bigger, the same light spreads over a larger area and the paper needs more exposure. The time grows with the square of the magnification plus one. Enter the negative width, 36 mm for 35 mm film or 56 mm for 6 × 6, the width of a print you already exposed well, its exposure time, and the new print width. For example, a good 16-second exposure for a 5-inch-wide print from 35 mm film becomes about 34.5 seconds at 8 inches wide. Always confirm with a test strip, because lens, paper and enlarger can add small differences.

f-stop test strips

The f-stop method, popularized by darkroom printer Gene Nocon, steps exposure in fractions of a stop rather than fixed seconds. Enter a base time and a step size of one sixth, one third or half a stop; the tool lists strip times centered on the base. With a 16-second base and third-stop steps, the strip runs 8, 10.1, 12.7, 16, 20.2, 25.4 and 32 seconds. Each step looks equally different on paper, so judging the best exposure and later dodging or burning by fractions of a stop becomes intuitive.

Chemistry dilutions

Bottles say “1+4” for fixer or “1+9” for paper developer. That means one part concentrate plus four or nine parts water. Enter how much working solution you need and the dilution, and the tool gives the volumes of concentrate and water. A liter of 1+4 fixer needs 200 ml of concentrate and 800 ml of water.

The audible timer

Each calculated time comes with a start button. The countdown clicks every second and plays a long tone at the end, so you can follow it in the dark without looking at the screen. It is generated in the browser with Web Audio, without files to download. You can pause and resume.

Using a phone or tablet in the darkroom

Screens emit light that can fog paper. Turn the brightness all the way down, use a dark mode, keep the device face down or far from the easel, and test with a safelight-style fog test if in doubt: lay a coin on a sheet of paper near the device for a few minutes, develop it, and check that no outline appears.

Practical printing workflow

Make a test strip at the base time, develop it fully, and pick the best step. If you change print size, rescale the time here, then make one confirming strip. Note the final time and settings on the back of the print or in a notebook for reprints.

Settings are remembered

The tool keeps your last inputs in the browser, so the next session starts where you left off.

Related tools

For alternative processes with digital negatives, use the Digital Negative Maker. For film exposure in pinhole cameras, try the Pinhole Camera Calculator. A general Online Timer helps with development and wash times.