Aspect Ratio Calculator
Find the exact ratio for any dimensions, or lock a ratio and calculate the matching width or height for your next video, image, or screen recording.
Step 1
Find the exact ratio
Step 2
Calculate a matching dimension
Uses the exact 16:9 ratio. Change either dimension to update the other.
No upload or account required. Values stay in this tab.
Why use this aspect ratio calculator?
- Reduces any positive whole-number dimensions with an exact GCD calculation
- Calculates a missing width or height from the locked ratio
- Includes presets for widescreen, vertical, square, classic, photo, and ultrawide formats
- Rejects scaled sizes that cannot preserve the exact ratio with whole pixels
- Validates zero and non-integer values and limits dimensions to 100,000 pixels
- Runs entirely in your browser without uploading or storing your values
Frequently asked questions
How do you simplify an aspect ratio?
Divide the width and height by their greatest common divisor. For 1920 × 1080, the greatest common divisor is 120, so the exact reduced ratio is 16:9.
How do I calculate a missing width or height?
Keep the ratio locked and enter either dimension. To find width, multiply the known height by ratio width divided by ratio height. To find height, multiply the known width by ratio height divided by ratio width. If the answer is not a whole pixel or exceeds the supported limit, choose another known dimension that is divisible by the relevant ratio side.
Why does an ultrawide resolution sometimes reduce to 43:18 instead of 21:9?
Marketing labels are often approximations. For example, 3440 × 1440 reduces exactly to 43:18, while 21:9 describes the broader ultrawide format family. The calculator reports the exact mathematical ratio for the numbers entered.
What aspect ratio should I use for video?
16:9 is the common choice for YouTube, presentations, and desktop video. Use 9:16 for Shorts, Reels, and TikTok, 1:1 for square posts, and 4:3 when matching classic slides or older footage.
Does aspect ratio depend on pixels or physical size?
No. Aspect ratio only compares width with height, so 1920 × 1080 and 1280 × 720 are both 16:9. Physical size and pixel density affect sharpness, but not the ratio.
Are my dimensions sent anywhere?
No. Every calculation uses simple math in your browser. The values you enter are not uploaded or stored by this tool.
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