Image-resize dimensions
Work out the matching height for a new width — or the matching width for a new height — so a resized image keeps its original proportions.
Result
New height (keeping aspect ratio)
Result
New width (keeping aspect ratio)
How to use this tool
- Enter the image's original width and height.
- Enter the new width you want.
- Read the matching height that keeps the image's proportions.
Assumptions
- Assumes you want to preserve the exact original aspect ratio — cropping to a different ratio needs a separate decision about what to cut.
Technical details: what the fields mean
- Original width
originalWidth - The image's current width in pixels.
- Original height
originalHeight - The image's current height in pixels.
- New width
newWidth - The width you want to resize to.
Methodology
New height = new width × (original height ÷ original width) — keeps the same width-to-height ratio as the original.
Worked example
1600×900px image resized to 800px wide
Inputs: Original width: 1600 px, Original height: 900 px, New width: 800 px
Result: 450px height
A 4000×3000 camera photo shrunk to 1200px wide for a website
Inputs: Original width: 4000 px, Original height: 3000 px, New width: 1200 px
Result: 900px high — 30% of the original in each direction, and about 9% of the file's pixels.
Height first: a 1920×1080 frame that must be 600px tall
Inputs: Original width: 1920 px, Original height: 1080 px, New height: 600 px
Result: 1067px wide (1066.7 rounded).
Practical guidance
- Most image editors and CSS frameworks have a 'lock aspect ratio' option that does this automatically — use this calculator when you need the exact number ahead of time.
- Shrinking is safe; enlarging beyond the original pixel size makes the image softer, because no new detail is created.
- If the result must hit an exact box (e.g. 1200×630), resize to cover the box and then crop the excess.
Common mistakes
- Manually entering both a new width and a new height without checking they match the original ratio, which stretches or squashes the image.
FAQs
How do I resize an image without distorting it?
Only specify one new dimension (width or height) and calculate the other using the original ratio — this calculator does that for you.
Why is the result sometimes off by a pixel?
Pixels are whole numbers, so the exact proportional size is rounded. A one-pixel difference isn't visible.
Last reviewed: 2026-09-25
Assumes preserving the original aspect ratio exactly — for a different target ratio, you'll need to crop rather than just resize.
This tool provides an indicative estimate, based on the assumptions stated above.
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