Image File Size Calculator
Calculate raw image size from width, height, and bit depth. Learn what the estimate includes, what it omits, and why it cannot predict a compressed file.
There is an exact answer for raw pixel data and no exact answer for a compressed file, and confusing the two is the most common mistake in file size planning. This calculator gives you the exact raw figure, shows the arithmetic behind it, and is explicit that your final JPG or WebP will land somewhere below it. Use it to plan storage, not to promise a byte count.
How it works
The exact calculation
The raw size is arithmetic with no uncertainty. Width times height gives the pixel count, and each pixel holds a fixed number of bits depending on its colour depth. Dividing by 8 converts bits to bytes, and that is the whole calculation. Everything a real file adds on top of this is extra.
raw bytes = (width × height × bits per pixel) ÷ 8
Bit depth options and what each one is for
Bit depth decides how many values each colour channel can take, and it is the multiplier in the formula. 8 bits per channel is the everyday choice, which is 24 bits per pixel for a photo with no transparency. Adding transparency needs one more channel, which is 32 bits per pixel. Professional colour work uses 16 bits per channel.
| Bit depth | Channels | Bits per pixel | Used by |
|---|---|---|---|
| 8 bit per channel | RGB | 24 bit | Everyday photos and screenshots |
| 8 bit per channel plus alpha | RGBA | 32 bit | Images with transparency, PNG exports |
| 16 bit per channel | RGB | 48 bit | Professional photo editing and scanning |
| 16 bit plus alpha | RGBA | 64 bit | Editing masters that keep transparency |
| 1 bit | Indexed | 8 bit worst case | Simple graphics and bilevel scans |
Why this is not a compressed file size
Raw pixel data is the ceiling, not a prediction. A lossy format discards detail the encoder judges unnecessary, and how much it discards depends on the content, the quality setting, and the encoder implementation. Two images of identical dimensions can differ several times over in output size. The only exact way to know is to encode the file and look, which is what the size checker and the target size compressor do.
NoteTreat this number as a storage planning figure. For a specific byte target, use a target size compressor that re-encodes until it fits.
What a real file adds on top
Every saved image carries more than pixel data. There is a file header describing dimensions and colour, often a colour profile, and any metadata such as camera details or GPS coordinates. Together these usually add a few kilobytes, which matters only for very small files. It is also why a zero pixel count does not produce a zero byte file.
- Header and dimension data: a few hundred bytes to a few kilobytes.
- Colour profile: several kilobytes when embedded.
- Metadata: highly variable, and it can be stripped with the EXIF remover.
Planning storage and uploads with the raw figure
The raw number is genuinely useful even though it does not predict output. It tells you whether an uncompressed workflow is viable at all, which is how you know if a lossless master fits on the device you are working from. It also gives you the worst case, so a disk that holds the raw size of every frame will never fill up unexpectedly.
Frequently asked questions
How do I calculate raw image size?
Multiply width by height to get the pixel count, multiply by the bits per pixel to get total bits, then divide by 8 for bytes. A 1,920 by 1,080 image at 24 bits is 2,073,600 pixels times 3 bytes, which is 6.22 MB raw.
Why is my JPG so much smaller than the raw figure?
Because JPG is lossy and compresses. The raw number is the uncompressed pixel data, before any format is applied. A photo of that size saved as a balanced quality JPG will usually be well under 1 MB.
Can this calculator tell me the size of a compressed file?
Not reliably. The compressed size depends on the encoder, the quality setting, and the content itself. A detailed landscape and a flat grey image at the same quality produce very different files. For an exact figure, check an actual file with the image size checker.
What is bits per pixel for a normal photo?
24 bits per pixel, which is 8 bits for each of red, green, and blue with no alpha channel. An image with transparency needs 32 bits per pixel. Higher depths such as 16 bits per channel exist for professional work and quadruple the raw size.
Does the raw size include file overhead?
No. Every image file also contains a header, colour profile, and metadata, which add a few kilobytes. That is why a very small raw size still produces a file of more than zero bytes.