Image Size Calculator: File Size, Megapixels and Print Size

Enter the width and height in pixels, the colour depth and an approximate compression ratio. The calculator gives the uncompressed size, an estimate of the compressed size, the megapixels, aspect ratio and the print size at your chosen dpi.

FreeNo sign-upRuns in your browserUpdated 2 Nov 2026
JPEG is often 8:1 to 20:1. PNG photos are around 2:1.
300 dpi is common for sharp prints.
Your resultLive

Estimates only. Check important results before you rely on them.

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How to use this calculator

  1. Enter the width and height in pixels.
  2. Choose the colour depth.
  3. Enter an expected compression ratio.
  4. Read the sizes, megapixels and print dimensions.

The formula

Uncompressed bytes = Width × Height × Bits per pixel ÷ 8. Compressed ≈ Uncompressed ÷ Ratio. Megapixels = Width × Height ÷ 1,000,000. Print size (inches) = Pixels ÷ dpi.

Worked example

A 4,000 × 3,000 photo is 12 megapixels. At 24 bits per pixel the uncompressed size is 36 MB. At a 10:1 compression, the file is about 3.6 MB. At 300 dpi it prints at 13.33 × 10 inches (33.9 × 25.4 cm).

Understanding your result

Real compressed sizes depend on the image content and quality setting, so the figure is an estimate. A noisy photo compresses less than a flat graphic.

When to use it

  • Estimate storage for photos and scans.
  • Check if a photo is large enough to print.
  • Plan image sizes for websites and uploads.

Assumptions and limits

File sizes are estimates. The tool does not account for metadata or specific formats.

Frequently asked questions

How do I calculate image file size?

Multiply width, height and bits per pixel, then divide by 8 to get bytes.

How many megapixels is 4000 × 3000?

12 megapixels.

What dpi is needed for printing?

300 dpi is common for sharp prints. 150 dpi may be acceptable for large posters.

Why is my JPEG smaller than the estimate?

Compression depends on the image. Smooth images compress much better.

What is colour depth?

The number of bits used for each pixel. 24-bit means 8 bits for each of red, green and blue.