Image dimensions tell you how many pixels wide and tall a raster image is. Aspect ratio describes the relationship between those two numbers. Checking both before you upload, resize or crop an image can prevent stretched images, unexpected cropping and unnecessary file sizes.
What image dimensions mean
An image described as 1600 × 900 has 1600 pixels of width and 900 pixels of height. These are the image's pixel dimensions. They do not directly tell you how many megabytes the file uses because file size also depends on format, image content and compression.
What aspect ratio means
Aspect ratio is the relationship between width and height. For 1600 × 900, dividing both values by 100 gives 16:9. For 1200 × 1200, the ratio is 1:1. Keeping the same ratio while resizing preserves the original shape.
Check dimensions with Tervilo
- Open the Tervilo Image Dimensions Checker.
- Select the image.
- Review width, height, aspect ratio, format and file size.
- Decide whether resizing, cropping or compression is the correct next step.
Example: a 16:9 source
A 1920 × 1080 image is 16:9. Resizing it to 1280 pixels wide while preserving the ratio produces 1280 × 720. Changing it to 1280 × 800 without cropping or padding would alter the shape and cause distortion if the pixels are simply stretched.
Dimensions vs resolution
Pixel dimensions describe the number of pixels in the image. “Resolution” can be used in several contexts, including pixel dimensions and print density such as DPI/PPI. For web uploads, pixel width and height are usually more directly relevant than a print-density number.
Dimensions vs file size
Two 1200 × 800 images can have very different file sizes. A detailed photograph, a flat-color illustration and a transparent PNG do not compress the same way. Check pixel dimensions separately from the number of bytes.
When should you resize?
Resize when the destination needs a smaller or specific pixel size. If the source is already the correct dimensions but the file is too large, compression or format conversion may be more appropriate.
When should you crop?
Crop when the required aspect ratio or composition differs from the source. For example, changing a wide landscape photo into a square may require removing pixels, not stretching the image.
Why checking before compression helps
If an image is dramatically larger in dimensions than the destination requires, resizing can reduce the amount of image data before compression. This often gives you more control over quality than forcing an oversized image through very aggressive compression.
Use the result with Tervilo's other image tools
After checking dimensions, use the Image Resizer for proportional scaling, the Image Cropper when composition must change, or the Image Compressor when dimensions are already appropriate but the file is too large.
Common mistakes
- Confusing pixel dimensions with file size.
- Changing width and height independently.
- Using DPI as a substitute for web pixel dimensions.
- Compressing an oversized image instead of resizing it.
- Ignoring the destination's required aspect ratio.
Quick checklist
- □ I recorded the width and height.
- □ I know the destination's required ratio.
- □ I distinguished pixel dimensions from file size.
- □ I chose resize, crop or compression based on the actual problem.
- □ I checked the final dimensions after processing.
Quick answer
Check an image's pixel width and height, then compare the aspect ratio with the destination requirement. Use resizing when scale is the problem, cropping when shape/composition is the problem, and compression when the dimensions are already appropriate but the file is too large.