Resizing images is one of the most common image editing tasks. Whether you need to fit a photo into a specific dimension for a website, prepare an image for printing, or shrink a large file for email, knowing how to resize properly ensures your images look sharp at any size.
This guide covers everything you need to know about resizing images online — from basic concepts to practical workflows using BestPNG's free image resizer.
Pixels, Dimensions, and Resolution
Before resizing, it helps to understand what you're actually changing.
Pixels are the individual dots that make up a digital image. A 1920x1080 image contains 1920 pixels across and 1080 pixels down — about 2 million pixels total.
Dimensions refer to the width and height in pixels. When you resize an image, you're changing these numbers.
Resolution (DPI/PPI) describes how many pixels fit per inch when printed. A 300 DPI image prints at higher quality than a 72 DPI image at the same dimensions. For screen display, resolution doesn't matter — only pixel dimensions do.
Pixels vs Percentage Resizing
There are two ways to specify a new size:
By Pixels
Specify exact width and height values. This gives you precise control over the output dimensions.
- Resize to 800x600 pixels
- Resize width to 1200 pixels (height auto-calculated)
Best for: web images with known display sizes, social media dimensions, specific print sizes.
By Percentage
Scale the image by a percentage of its current size.
- Resize to 50% (halves both dimensions)
- Resize to 200% (doubles both dimensions)
Best for: batch processing where you want consistent scaling, quick reductions without calculating exact pixels.
Maintaining Aspect Ratio
Aspect ratio is the proportional relationship between width and height. A 1920x1080 image has a 16:9 aspect ratio. A 2000x2000 image is 1:1 (square).
Always maintain aspect ratio unless you specifically need a different proportion. Changing width without proportionally changing height (or vice versa) distorts the image — stretching or squashing the subject.
When using BestPNG's resizer, aspect ratio is locked by default. Enter either width or height, and the other dimension adjusts automatically. You can unlock it if you need a specific non-proportional size, such as cropping for a social media cover.
Upscale vs Downscale
Downscaling (Making Smaller)
Reducing image dimensions is simple and always produces good results. The resizer averages neighboring pixels to create a smaller, sharp output. A 4000x3000 photo downscaled to 1200x900 will look clean and crisp.
Upscaling (Making Larger)
Enlarging an image is more challenging because you're asking the software to create pixel data that doesn't exist. Traditional upscaling (bilinear/bicubic interpolation) adds pixels by averaging neighbors, which results in a softer, blurrier image.
For significant upscaling (2x or more), AI-powered tools produce much better results. BestPNG's upscale tool uses AI to intelligently fill in detail when enlarging images.
Rule of thumb: Downscaling is safe at any ratio. Upscaling beyond 2x without AI assistance will noticeably degrade quality.
How to Resize Images with BestPNG
BestPNG's image resizer works directly in your browser — no upload to a server, no signup needed.
Step-by-step:
- Open BestPNG's resize tool
- Upload your image (PNG, JPG, WebP supported)
- Choose your resize method:
- Enter a specific width or height in pixels (the other auto-adjusts with aspect ratio locked)
- Or enter a percentage to scale proportionally
- Preview the resized image
- Download the result in your preferred format
Tips for Best Results
- For web: Resize to the actual display width (or 2x for retina support)
- For email: 600-800px width is well-suited for most email clients
- For printing: Calculate pixels from your target print size and DPI (e.g., 8x10 inches at 300 DPI = 2400x3000 pixels)
- For social media: Use the platform-specific dimensions (see our social media sizing guide)
Batch Resizing
Need to resize dozens or hundreds of images to the same dimensions? BestPNG supports batch resizing — drop multiple files, set your target size once, and process them all.
This is particularly useful for:
- E-commerce: Standardizing product photo dimensions across a catalog
- Photo galleries: Creating consistent thumbnail sizes
- Web development: Generating multiple responsive image sizes
- Presentations: Fitting images to slide dimensions
Output Formats
When resizing, you can also choose the output format:
| Format | Best For | Transparency |
|---|---|---|
| PNG | Graphics, text, screenshots | Yes |
| JPG | Photos, images without transparency | No |
| WebP | Web use (smaller files) | Yes |
If your original is a PNG with transparency, keep it as PNG. If it's a photo for web use, consider outputting as WebP for smaller file sizes. BestPNG handles format conversion during the resize process.
Common Resizing Mistakes
Mistake 1: Not maintaining aspect ratio. Stretching an image to fit a non-proportional frame distorts the subject. Crop instead of stretch.
Mistake 2: Upscaling low-resolution images. A 200x200 thumbnail upscaled to 2000x2000 will look blurry regardless of the tool. For significant enlargement, use an AI upscaler.
Mistake 3: Resizing without compressing. A resized image may still have a large file size if not compressed. After resizing, use the compress tool to optimize file size.
Mistake 4: Using the wrong dimensions for the platform. Social media platforms have specific dimension requirements. Using the wrong size means the platform will crop or pad your image unpredictably.
Frequently Asked Questions
Does resizing reduce image quality? Downscaling (making smaller) preserves quality well. Upscaling (making larger) beyond 2x degrades quality unless you use AI upscaling. The resize algorithm also matters — bicubic and Lanczos produce sharper results than bilinear.
What dimensions should I use for my website?
For content images, 800-1200px wide is typical. For hero/banner images, 1600-2400px wide. Always consider serving 2x dimensions for retina displays via srcset.
Can I resize and compress at the same time? BestPNG's resize tool handles the dimension change. For additional file size reduction, run the result through the compress tool. The two-step workflow (resize then compress) gives you the most control.
How do I resize an image for email? Resize to 600px width for email body images (most email clients display at this width). For email headers, 600-700px works for most templates. Then compress to keep the file under 200 KB.
What is the difference between resizing and cropping? Resizing changes the dimensions of the entire image (all content is preserved, just scaled). Cropping removes parts of the image to create a smaller frame. Use resizing when you want to keep everything in the image; use cropping when you want to focus on a specific area.
Conclusion
Resizing images is simple when you understand the basics: maintain aspect ratio, resize to your target dimensions, and choose the right output format. For most tasks, BestPNG's image resizer handles everything in seconds — directly in your browser, free, and without any signup.
For web use, pair resizing with compression to get the smallest possible file size. For enlarging small images, use the AI upscaler instead of a standard resize.