How to Use This Tool
Enter your camera's megapixels and card size. RAW is calculated; JPEG is given as a range, because a single number there would be dishonest.
Why RAW can be calculated and JPEG cannot
A RAW file is close to the sensor's raw output: one value per photosite at the sensor's bit depth. So 24 million pixels at 14 bits is about 42 MB uncompressed, and that is the same whatever you point it at. Lossless compression brings it down — typically to around 60–70% — but the variation stays small.
JPEG discards information based on what the eye notices, and how much it can discard depends entirely on the scene. Smooth gradients compress enormously; fine random detail barely compresses at all. The same camera can produce a 4 MB file of an overcast sky and a 12 MB file of a hedge. Any tool giving you one JPEG number has picked a scene on your behalf without saying so.
What actually changes RAW size
- Megapixels — linear. Double the pixels, double the file.
- Bit depth — 12-bit is a fifth smaller than 14-bit and holds less shadow information. Many cameras drop to 12-bit automatically in fast burst modes, which is worth knowing before it happens.
- Compression setting — lossless compressed is the usual sensible default. Lossy compressed RAW saves a lot more and discards data you may want when recovering highlights.
- Not the ISO or the subject, much. High ISO adds noise, which is random detail and compresses badly, so files grow a little — but nothing like the JPEG variation.
How many cards to take
A rule that survives contact with reality: work out the count, then halve it for planning. People shoot far more than they expect when something is actually happening, bursts fill space in seconds, and discovering a full card mid-event costs more than a spare card does.
Two cards of half the size also beat one large one, for a reason that has nothing to do with capacity: a card failure loses everything on it, and splitting the shoot across two halves the worst case.
RAW plus JPEG
Shooting both writes two files per shot, so capacity is roughly RAW size plus JPEG size — often around 1.3 times RAW alone. It is worth it when you need something to send immediately and want the RAW for later. It is not worth it if the JPEGs will be deleted unlooked-at, which is what usually happens.
