Image Size Calculator
Enter the width and height in pixels, the bit depth and the file format. The calculator works out the uncompressed size, estimates the saved file size and shows megapixels and aspect ratio.
- Pixels to megabytes
- PNG, JPEG and WebP
- Aspect ratio
Compression ratios are typical for photos. Flat graphics and screenshots compress much better as PNG.
Uncompressed size is simple maths; saved size depends on the format. Every pixel in a normal colour image takes 24 bits, or 3 bytes. A 4000 × 3000 photo is 36 MB in memory. Saved as a JPEG it might be 5 MB, and as WebP about 2 MB, because those formats throw away detail you are unlikely to notice.
Common image sizes
Pixels and uncompressed size. Search for a size.
| Use | Pixels | Megapixels | Uncompressed |
|---|---|---|---|
| Instagram square | 1080 × 1080 | 1.2 | 3.5 MB |
| Instagram portrait | 1080 × 1350 | 1.5 | 4.4 MB |
| Full HD | 1920 × 1080 | 2.1 | 6.2 MB |
| Website hero | 2400 × 1200 | 2.9 | 8.6 MB |
| 4K UHD | 3840 × 2160 | 8.3 | 24.9 MB |
| 12 MP phone | 4032 × 3024 | 12.2 | 36.6 MB |
| 24 MP camera | 6000 × 4000 | 24 | 72 MB |
| 48 MP phone | 8064 × 6048 | 48.8 | 146 MB |
Social platforms resize uploads to these dimensions. Uploading at exactly the right size avoids a second round of compression.
Megapixels and file size
24-bit colour. Slide the megapixels.
File size grows in step with pixel count. Doubling both width and height makes the file four times bigger.
How to work out image size
From pixels to bytes. Step through it.
Count pixels
Width × height. 4000 × 3000 = 12,000,000.
Resizing a photo for the web to 2000 pixels wide and saving as WebP or JPEG at 80% usually gives files under 300 KB with no visible loss.
JPEG, PNG or WebP
Pick the format for the image. Compare the formats.
Lossy compression made for photos. Universally supported.
Lossless. Keeps every pixel exactly, so files are large for photos.
Modern lossy or lossless format, smaller than JPEG at the same quality.
AVIF is newer still and often 20% smaller than WebP, but older software may not open it.
Preparing images for the web
Fast pages and sharp pictures. Tick each item.
Tick each item as you go.
Large images are the most common cause of slow pages. Serving them at the display size, not the camera size, can cut page weight by 90%.
What you get
Size, pixels and shape. Each tile explains one result.
Estimated size on disk.
Uncompressed size while editing.
Millions of pixels.
Width to height, reduced.
Bits stored for each pixel.
Aspect ratio stays the same when you resize proportionally. Cropping changes it.
Frequently Asked Questions
No question matches that search.
How do I calculate image file size?
Multiply width × height × bit depth, then divide by 8 for bytes. Compressed formats are a fraction of that.
How big is a 12 megapixel photo?
36 MB uncompressed, about 3 to 5 MB as a JPEG.
What is the difference between pixels and DPI?
Pixels are the image's resolution. DPI only matters when printing and sets how big those pixels appear on paper.
Is PNG bigger than JPEG?
For photos, yes, usually three to five times. For simple graphics PNG can be smaller.
How can I make an image file smaller?
Resize it to the size it will be shown, save as WebP or JPEG at about 80% and strip metadata.
What does 24-bit colour mean?
8 bits each for red, green and blue, giving about 16.7 million colours.
What size should images be for a website?
Usually 1200 to 2400 pixels wide and under 300 KB.
Right-size every image
Pixels times bit depth gives the raw size, and the format decides how much of that you keep. Resize to the display size, pick a modern format and your images will look sharp and load fast.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.