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Image Resize Calculator

Keep the proportions: change one side or a percentage and get the other side.

px
px

New size

1200 × 900px

Scale

Not to scale

All results
Exact (before rounding)1,200 × 900px
Scale30%
Aspect ratio (kept)4:3
Megapixels12 → 1.08

To resize without distortion, scale both sides by the same factor. A 4000 × 3000 photo resized to 1200 px wide is 1200 × 900, a factor of 30%. Give a new width, height or percentage and the other side is calculated and rounded.

How it works

new height = new width × height ÷ width

new size = size × percent ÷ 100

Worked example

With a 4000 × 3000 px image resized to 1200 px wide:

  1. Scale factor: 1,200 ÷ 4,000 = 0.3.
  2. Width: 4,000 × 0.3 = 1,200 → 1200 px.
  3. Height: 3,000 × 0.3 = 900 → 900 px.

When you need this tool

Preparing images for a website, a social post, an email or a slide. You usually know one target dimension (“the column is 1200 px wide”) and need the other one to keep the image from stretching.

How it works

The scale factor is the new width divided by the original width (or the same for height, or the percentage ÷ 100). Both sides are multiplied by it, then rounded to whole pixels, half up.

Sizes for common uses

  • Blog or article image: 1200–1600 px wide
  • Full-width hero on desktop: 1920–2560 px wide
  • Email images: 600 px wide (1200 px for high-density screens)
  • Open Graph share image: 1200 × 630 px

File size scales with area

Halving the width and height leaves a quarter of the pixels, so the file is roughly a quarter of the size too. The calculator shows megapixels before and after so you can see the saving.

Common mistakes

Resizing only one side. Changing width without height squashes or stretches the image.

Upscaling to fit. A 800 px image stretched to 1600 px looks blurry. Start from a larger original if you have one.

To find the shape first, use the aspect ratio calculator.

Questions

How do I keep the aspect ratio when resizing?

Multiply both width and height by the same factor: new width ÷ old width. Most editors do this when the chain or lock icon is on.

What size should images be for a website?

No larger than they're displayed, times 2 for high-density screens. A 600 px wide content image needs about 1200 px of real width.

Does resizing reduce quality?

Making an image smaller keeps it sharp. Making it bigger (upscaling) can't add detail, so it looks soft.

How do I resize to a percentage?

Choose Percentage and enter, for example, 50 to halve both sides.

Last reviewed 2026-09-24. How we check values · Report a problem with this page