Online tools New Zealand
Resize Image Online
Forms ask for a photo of a particular size, social platforms crop anything that is the wrong shape, and big photos make slow pages. This tool resizes images to the width and height you give, or by a percentage, using your browser, so nothing is uploaded. Built for New Zealand users, with nothing sent to a server.
Free, no signup Runs in your browser
Result
—Files
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Original size
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New size
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Saved
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Your files
How do I resize an image to a specific size?
Choose the image and set the width, or both width and height, in pixels. Setting only the width keeps the shape of the picture because the height is worked out for you; setting both stretches the image if the proportions differ. A percentage option scales everything by the same amount.
Common sizes
Web page images rarely need to be more than about 1,600 pixels wide. Social platforms have their own preferred sizes, which change often, so check the platform's current guide. Passport and licence photos have set dimensions in millimetres, which depend on print size as well as pixels, so use the issuing agency's tool for those.
Email attachments and upload forms often limit file size, which resizing reduces the most.
Resizing and quality
When reducing, the tool uses the browser's high-quality smoothing. Saving as JPG or WebP with quality 85 to 90 retains detail; PNG preserves everything but gives larger files. Transparent areas become white when saving as JPG.
To reduce file size without changing the dimensions, use the compress image tool.
How this is calculated
The rule, step by step, so you can check any figure by hand.
new size from the width you give: height = original height × new width ÷ original widthpercentage: both sides × the percentageexact: the width and height you enter, which stretches the image if the shape differsthe image is redrawn on a canvas with high-quality smoothing and saved
Reducing an image is safe because detail is only discarded. Enlarging is different: the extra pixels are interpolated guesses, so an enlarged photo looks soft rather than sharper. If you need a bigger print, start from a bigger original.
Keeping the aspect ratio avoids distortion. Exact sizes that do not match the original's shape stretch the picture, so crop first if you need a specific shape such as a square avatar.
A worked example
A 4,032 × 3,024 photo resized to 1,200 pixels wide.
- Aspect ratio4:3
- New height, 3,024 × 1,200 ÷ 4,032900 pixels
- File sizefrom about 4 MB to about 250 KB
A 1,200 × 900 image about one sixteenth the size of the original.
The tool shows the exact new size and file size.
Privacy
Your images never leave your device. If a photo contains people's personal information, working locally avoids a copy being stored elsewhere, which fits the Privacy Act 2020.
What it leaves out
There is no crop, rotate or filter. Metadata such as location is removed on export.
What this calculator does not do
- No cropping or rotating
- Enlarging does not add detail
- Very large images depend on device memory
- Animated images lose their animation
Common questions
How do I resize an image without losing quality?
Reduce it rather than enlarge it, and save as PNG or at high JPG quality.
How do I keep the same shape when resizing?
Use the width option, which works out the height from the original shape.
What size is best for a website?
Usually under 1,600 pixels wide and under 300 KB.
Is my image uploaded?
No, resizing runs in your browser.
Can I resize several images at once?
Yes. Each gets its own download link.
Where these numbers come from
- MDN — HTMLCanvasElement.toBlob How browsers encode canvas pixels to JPEG, PNG and WebP
- Office of the Privacy Commissioner New Zealand's privacy regulator, for the Privacy Act 2020
Method last reviewed 2026-10-28 This calculator uses fixed rules rather than rates that change, and its method is re-checked against the sources above at least once a year. Out of date? Tell us and we will fix it.
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