Free Live Calculators

Aspect Ratio Calculator — Find, Convert & Resize

Find the simplified aspect ratio from width and height, solve for a missing dimension from a target ratio, or resize proportionally without distortion.

Simplified Ratio
16:9
Decimal: 1.7778

Find Ratio simplifies width:height using the greatest common divisor. Ratio → Dimension solves for a missing side given a target ratio. Resize Proportionally scales one dimension while keeping the original width:height proportions intact — useful for resizing images or video without distortion.
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Reference Values

Last verified:
Category Range What It Means Status
16:9 (Widescreen) ★ e.g. 1920×1080, 3840×2160 Standard for YouTube, most TVs, monitors, and streaming video since HD became the norm. ★ Best
4:3 (Standard/Classic) e.g. 1024×768, 800×600 Older TV and monitor standard, still used for presentations, some tablets, and legacy content. Good
9:16 (Vertical/Portrait) e.g. 1080×1920 Standard for Instagram/TikTok Stories, Reels, and Shorts — the rotated equivalent of 16:9. Good
21:9 (Ultrawide/Cinematic) e.g. 2560×1080, 3440×1440 Common for ultrawide monitors and cinematic film presentation. Okay
1:1 (Square) e.g. 1080×1080 Standard square format for Instagram feed posts and profile images. Okay

Source: Common industry-standard aspect ratios for video, photography, and display formats

Worked Examples

Find Ratio: 1920×1080

Width
1920 px
Height
1080 px
16:9

GCD(1920, 1080) = 120. 1920 ÷ 120 = 16, 1080 ÷ 120 = 9 — the standard widescreen ratio.

Find Height: 16:9 Ratio, Width 1280

Ratio
16:9
Width
1280 px
Height = 720 px

Height = Width × (ratio height ÷ ratio width) = 1280 × (9 ÷ 16) = 720.

Resize Proportionally: 1920×1080 to Width 1280

Current
1920×1080
New Width
1280 px
New Height = 720 px

New Height = New Width × (Current Height ÷ Current Width) = 1280 × (1080 ÷ 1920) = 720 — keeps the same 16:9 proportions.

Find Ratio: 3440×1440 (Ultrawide Monitor)

Width
3440 px
Height
1440 px
43:18

GCD(3440, 1440) = 80, giving 43:18 — not a perfectly round number, though it's commonly described as 'approximately 21:9' since it's close to double a 21.5:9-style ultrawide ratio.

How to Use This Calculator

  1. 1

    Choose a mode

    Find Ratio (from pixel dimensions), Ratio → Dimension (solve for a missing side), or Resize Proportionally (scale without distortion).

  2. 2

    Enter your known values

    Input fields adjust based on your selected mode.

  3. 3

    Use a common ratio quick-pick if applicable

    16:9, 4:3, 9:16, 21:9, 1:1, 3:2, and 5:4 are available as one-click options in Ratio → Dimension mode.

  4. 4

    Read the result and visual preview

    A scaled rectangle preview shows the resulting proportions alongside the calculated numbers.

What Each Value Means

Simplified Ratio (w:h)
Width and height reduced to their smallest whole-number equivalent by dividing both by their greatest common divisor (GCD) — 1920×1080 simplifies to 16:9.
Proportional Resize (pixels or any unit)
Calculating a new width or height that preserves the exact same width-to-height ratio as the original dimensions, preventing visual stretching or squashing.

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Frequently Asked Questions

How do you find the aspect ratio from width and height?
Divide both width and height by their greatest common divisor (GCD). For 1920×1080: GCD(1920, 1080) = 120, so 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, giving a 16:9 ratio. This works for any pixel dimensions, not just standard video/photo sizes.
How do you find a missing dimension from an aspect ratio?
If you know the width and want the height for a target ratio: Height = Width × (ratio height ÷ ratio width). For a 16:9 ratio with a 1280 width: 1280 × (9 ÷ 16) = 720. Reverse the fraction to solve for width given a known height instead.
How do you resize an image or video proportionally without distorting it?
Calculate the new dimension using the same ratio as the original: New Height = New Width × (Original Height ÷ Original Width). For a 1920×1080 image resized to a 1280 width: 1280 × (1080 ÷ 1920) = 720 new height. Using any other height would stretch or squash the image.
What's the difference between 16:9 and 21:9?
16:9 is standard widescreen (used by YouTube, most TVs, and monitors) — a ratio of about 1.78:1. 21:9 is ultrawide/cinematic format — a ratio of about 2.33:1, noticeably wider relative to its height. Many 'ultrawide' monitors advertised as 21:9 are actually closer to other ratios like 43:18 when measured exactly, but are commonly described as 21:9 since it's the nearest well-known standard.
Why doesn't my calculated ratio come out to a clean number?
Not every pixel dimension simplifies to a well-known ratio. A 3440×1440 ultrawide monitor, for example, simplifies via GCD to exactly 43:18 — not a round number, even though it's commonly described as 'approximately 21:9.' This is normal and doesn't mean anything is wrong with your dimensions; it just means the exact pixel count doesn't perfectly match a standard named ratio.