DOKUNTAG Solution Guide

How to resize a photo to exact pixels, mm or cm on iPhone

Resize an iPhone photo using exact px, percentage, mm or cm values, while checking the aspect ratio and avoiding accidental distortion.

Search intent: Problem solving: prepare a photo for an exact digital or physical dimension.Last reviewed: September 29, 2026

Quick answer

The shortest useful answer

Use pixels when a website gives a digital dimension such as 600×600 px. Use mm or cm when the requirement is expressed as a physical size. Image Tools DOKUNTAG supports px, %, mm and cm resizing and lets you set the DPI used to translate a physical size into pixels.

How to

Step by step

Identify the unit used by the destination: px, mm, cm, or percentage.
Choose the photo and enter the required width and height.
Check whether the target ratio matches the source before forcing both dimensions.
Review the output and save a new file instead of overwriting the original.

What is the difference between pixels and millimetres?

Pixels describe digital image dimensions. Millimetres and centimetres describe a physical size, but a physical size becomes a pixel count only after a DPI value is chosen. Image Tools exposes that DPI setting instead of silently assuming that px and mm are interchangeable.

How do you avoid stretching the photo?

Compare the source and target aspect ratios first. If they differ, cropping is usually safer than stretching. The DOKUNTAG Aspect Ratio Calculator can show the ratio and the proportional height for a new width before you edit the image.

Which value should you solve first: dimensions or file size?

If the destination specifies both, prepare the required dimensions first and then reduce the file size. Changing dimensions after compression can change the final KB/MB result again.

Free web tools

Check it in the browser first

Check the source and target aspect ratioCheck image pixel dimensions

DOKUNTAG solution

Image Tools DOKUNTAG

To finish this workflow on your phone, open the official DOKUNTAG app page to verify current features, privacy behavior, and the live store link in one place.

Open app details Open in the App Store

Next step

Reduce the resized photo to a target KB/MB