Reduce a familiar resolution
1920 and 1080 share a greatest common divisor of 120. Dividing both by 120 gives 16:9. The same proportion appears at 1280 × 720 and 3840 × 2160.
Start with dimensions or a ratio
Use whole pixels, or enter ratio parts such as width 16 and height 9.
Resize while keeping the ratio
Even rounding affects only the calculated side. If a video encoder requires both sides to be even, also enter an even known dimension.
Your proportions
Reduced width : height
16:9
1.7778:1 · Landscape
New whole-pixel size
1,000 × 563
Exact height: 562.5 px
Scale: 0.5208×. Aspect-ratio change after rounding: -0.0888%. Calculated sizes are at least 1 pixel, or 2 pixels with even rounding.
For an exact 16:9 ratio with whole pixels, choose a width that is a multiple of 16 and a height that is the same multiple of 9.
Dimensions are calculated locally in your browser. No image upload is required.
How to use the Aspect Ratio Calculator
- 01
Enter the original width and height as whole pixels, or enter ratio parts such as 16 and 9.
- 02
Choose whether you know the new width or new height, then enter that dimension.
- 03
Pick a rounding method. Copy the reduced ratio and resized dimensions after checking any rounding error.
Examples
Resize a 16:9 image to 1,000 pixels wide
The exact height is 1000 × 9 ÷ 16 = 562.5 pixels. Nearest whole-pixel rounding gives 1000 × 563. A width of 1008 instead gives an exact whole-pixel height of 567.
Prepare a portrait layout
For a 9:16 ratio and a new height of 1920, the matching width is 1080 pixels. Swap orientation to compare the portrait and landscape proportions.
Reduce width and height to a ratio
Aspect ratio is width divided by height, usually written as width:height. To express whole-number dimensions in their simplest form, divide both by their greatest common divisor. A square is 1:1. A landscape image has a ratio above 1 when written as a decimal; a portrait image has a ratio below 1.
Calculate the missing dimension
For a known new width, new height = new width × original height ÷ original width. For a known new height, new width = new height × original width ÷ original height. These formulas preserve the original proportion before rounding. To preserve a reduced a:b ratio exactly with whole pixels, use a × k by b × k for a positive whole-number k.
Rounding for images and video
Raster files need whole-pixel dimensions. This calculator can round the missing side up, down, to the nearest whole pixel, or to the nearest even pixel. Even rounding may help with encoders that require even dimensions, but the known side stays unchanged. A nonzero aspect-ratio change means the rounded dimensions differ slightly from the source proportion.
A ratio does not choose a crop
Changing a 4:3 image into a 16:9 frame requires a layout decision: crop content, add empty space, or distort the image. This tool calculates proportional dimensions and does not edit files or select a crop. Use an image editor when the composition needs to change.
What to know
- Uses positive whole-number dimensions, up to 1,000,000,000 pixels per side. Calculated dimensions are also bounded to that maximum.
- Assumes square image pixels. The illustration is a shape preview, not a file resize or crop.
Common questions
Can I enter 16 and 9 instead of a full resolution?
Yes. The top fields accept ratio parts as well as pixel dimensions. Both are positive whole numbers, so 16 and 9 represent the same shape as 1920 and 1080.
Why does 21:9 reduce to 7:3?
Both 21 and 9 are divisible by 3. The reduced mathematical ratio is 7:3. A display marketed as ultrawide may use a resolution with a slightly different exact ratio, so enter its actual pixels when precision matters.
What does the rounding percentage mean?
It is ((new width ÷ new height) ÷ (original width ÷ original height) − 1) × 100. Positive means the rounded result is slightly wider in proportion; negative means it is slightly narrower.
Can I use this ratio in CSS?
Yes. A 16:9 shape can be expressed as aspect-ratio: 16 / 9. CSS layout constraints still influence the element’s final size; the calculator only provides the numerical proportion.