What is the largest possible print size from 35mm film?
There is no clear answer to your question as it depends on multiple factors, namely:
Film’s ability to record fine detail or resolution, which in turn consists of:
- resolving power (function of particle density in the emulsion)
- granularity (function of particle clumping in the emulsion)
- sharpness (perceived edge distinction)
The resolution depends on:
- camera quality (lens mount and film plane alignment, etc)
- lens quality (resolution and amount of aberrations)
- film type (different films of same speed have different resolution)
- film speed (granularity increases with speed)
- exposure (overexposure leads to more granularity)
- film processing (handling, developer, conditions, etc)
- film age and archival conditions
Also different methods of judging resolution lead to different results, magnification under loupe or microscope is different from enlargements which in turn is different from scanning and printing.
Kodak has published print grain indexes for their Portra line, says that the grain of 35mm Portra 160 film is visible already in 4×6” (10x15cm) prints, However, without visual comparison or experience this does not mean a lot.
Finally, the viewing distance plays very important role in how big you can print from a 35mm film, the further the viewing distance, the larger the print can be printed without loss of quality.
From a good quality 35mm film, stored correctly, you should be able to get prints of around 19″ longest edge at 300ppi, with a typical viewing distance of less than 16″.