How to Resize an Image — Free on Mac, iPhone, Android & Browser
How to resize an image comes up constantly — whether you are hitting a file size limit, need exact pixel dimensions for a social platform, or just want to save space. This guide covers every platform, no Photoshop required.
Quick answer: To resize an image in any browser, go to rapidtools.online/resize-image, upload your image, enter the width and height in pixels (or a percentage), click Apply Resize, then Download Resized Image. A PNG stays a PNG (with transparency) and a JPEG stays a JPEG; other formats, such as WebP, are saved as JPEG. On Mac: Preview → Tools → Adjust Size. On iPhone and Android, the Photos apps do not resize to exact pixels — use the browser tool.
These are two different operations that are easy to confuse:
R
Resize — changes dimensions while keeping all the content
The entire image gets scaled up or down. A 4000×3000 photo resized to 1000×750 shows the same content, just smaller. Used for hitting file size limits, social media dimension requirements, and storage reduction.
C
Crop — removes edges while keeping the remaining pixels at original scale
A 4000×3000 photo cropped to a square removes the left and right edges. The subject in the middle stays the same size — just the surrounding content is cut away. Used for changing the aspect ratio or removing unwanted edges.
💡 To change both: Crop to your desired aspect ratio first, then resize to the exact pixel dimensions you need.
1
Free Browser Tool — Any Device, Exact Dimensions
The most precise method — you choose the exact output size in pixels. Works on Mac, Windows, Chromebook, iPhone, and Android without installing anything, and your image never leaves your device.
Drag in a JPEG, PNG, or WebP, or click to choose one.
3
Choose how to resize
By Pixels: type a width or height. With “Maintain aspect ratio” ticked, the other number fills in for you. By Percentage: for example 50 for half size. Social Media Presets: one tap fills in a size such as Instagram Square (1080 × 1080).
4
Set the quality
For JPEG output, the Output Quality slider starts at 85%. Lower it for a smaller file, or raise it to keep more detail. PNG files are saved without loss, so the slider does not change them.
5
Click Apply Resize, then Download Resized Image
A preview shows the new size and file size before you download.
⚠️ Two things to know: the tool keeps your format where it can — a PNG stays a PNG with its transparency, and a JPEG stays a JPEG. Other formats, such as WebP, are saved as JPEG, where transparent areas become white. And a preset sets an exact width and height, so a photo with a different shape is stretched — crop it to the same ratio first with Crop Image.
ℹ️ Built-in presets: Instagram Square (1080 × 1080), Instagram Portrait (1080 × 1350), Facebook Post (1200 × 630), Twitter Post (1200 × 675), Full HD (1920 × 1080), and Email Friendly (800 × 600).
2
Mac Preview — Built Into Every Mac
Preview's Adjust Size dialog is the easiest way to resize an image on Mac without any extra software. It gives you exact pixel control and shows the resulting file size before you save.
1
Open the image in Preview
Double-click the file, or right-click → Open With → Preview.
2
Go to Tools → Adjust Size
The Adjust Size dialog opens. Change the unit dropdown from inches to "pixels" to work in pixel dimensions.
3
Enter the new width or height
Keep "Scale proportionally" checked to resize without distortion. Enter one dimension and the other updates automatically. Uncheck it if you need to force specific width and height (can distort).
4
Check the resulting file size and click OK
Preview shows the estimated file size at the bottom of the dialog. Click OK to apply.
5
Save with Cmd+S
Or File → Export to save a copy while keeping the original untouched.
💡 Batch resize on Mac: Select multiple images in Finder → right-click → Open With → Preview. In Preview, select all images (Cmd+A), then Tools → Adjust Size. This resizes all selected images at once.
3
iPhone — Use the Browser Tool in Safari
The iPhone Photos app crops but does not resize to exact pixels. The browser tool is the simplest free way.
The Resize and Skew dialog opens. Select "Pixels" instead of "Percentage".
3
Enter the new width (height auto-updates if "Maintain aspect ratio" is checked)
Click OK to apply.
4
Save with Ctrl+S
Or File → Save As to save a copy in a different format.
💡 Paint limitation: Paint saves JPEGs at a fixed compression level and has no quality control. For high-quality output (passport photos, print), use the browser tool instead.
How to Get an Image Under a File Size
Forms and email often reject images over a limit such as 1 MB or 2 MB. Two settings in the browser tool bring the file size down:
Make it smaller: a photo 1200 pixels wide is sharp on any screen and much smaller than a 4000-pixel original.
Lower the quality: for a JPEG, moving the Output Quality slider from 85% to about 70% often shrinks the file a lot with little visible change. A PNG keeps every detail, so if it is still too large, make it smaller in pixels.
Check the preview: the File Size line shows the result before you download, so you can adjust and try again.
💡 Work from the original photo each time. Resizing an already-compressed JPEG again and again adds blur and blocky artifacts.
Common Target Sizes
Use case
Target size
Notes
Instagram square post
1080 × 1080 px
1:1 — the Instagram Square preset
Instagram portrait post
1080 × 1350 px
4:5 — takes more space in the feed
Facebook link or post image
1200 × 630 px
The Facebook Post preset
X (Twitter) post image
1200 × 675 px
16:9 — the Twitter Post preset
Profile photo
400 × 400 px
Square; a safe size for most platforms
US passport photo
600 × 600 px minimum
Square — see the passport photo guide for the full rules
YouTube thumbnail
1280 × 720 px
16:9; YouTube allows up to 2 MB
Email attachment
About 1200 px wide
Readable on any screen and much smaller than the original
Resize Image Free — Exact Pixel Dimensions
Set any width and height, or use a social media preset. Works in any browser, and your file never leaves your device.
✓ Exact pixel control✓ Social media presets✓ File never uploaded✓ No watermark
Frequently Asked Questions
Making an image smaller keeps it sharp, because you are only removing pixels. Making it larger softens it, because new pixels have to be guessed. A PNG is saved without loss. A JPEG is saved again at the quality you choose (85% by default), so keep the slider high when detail matters.
Keep “Maintain aspect ratio” ticked, so the height changes with the width. If you need a different shape — for example a 4:3 photo in a 1:1 square — crop it to that ratio first, then resize.
Resizing changes the width and height in pixels. Compressing makes the file smaller by storing the same pixels more efficiently. In RapidTools you can do both at once: set a smaller size and lower the Output Quality slider.
Open rapidtools.online/resize-image in Safari, upload your photo, type the width or height, tap Apply Resize, then Download Resized Image. The iPhone Photos app crops but does not resize to exact pixels.
Yes. Resize Image saves a PNG as a PNG, so transparent areas stay transparent. Upload your PNG, set the size, and download. Other formats, such as WebP, are saved as JPEG, which has no transparency.
Resize it to about 1200 pixels wide, then lower the Output Quality slider until the File Size line in the preview is under 1 MB. Most JPEG photos get there with little visible change. The slider only affects JPEG files, so a large PNG needs a smaller width instead.
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