What This Calculator Does
This aspect ratio calculator computes the simplified ratio between width and height dimensions. It also provides a resize tool that lets you enter a new width or height and automatically calculates the other dimension to maintain the same proportions. A visual preview shows the shape of the ratio.
Inputs Explained
- Width (px): The horizontal dimension of your image, video, or screen in pixels.
- Height (px): The vertical dimension in pixels.
- Common Presets: Quick buttons for standard ratios like 16:9, 4:3, 1:1, 9:16, and 21:9.
- New Width / New Height (Resize Tool): Enter one value and the other is calculated to preserve the aspect ratio.
How It Works
The calculator finds the Greatest Common Divisor (GCD) of the width and height using the Euclidean algorithm, then divides both dimensions by the GCD to produce the simplified ratio. For the resize tool, it uses the proportion formula: new height = new width × (original height ÷ original width), and vice versa.
Formulas Used
GCD = Euclidean algorithm applied to Width and Height
Simplified Ratio = (Width ÷ GCD) : (Height ÷ GCD)
Decimal Ratio = Width ÷ Height
Resize: New Height = New Width × (Original Height ÷ Original Width)
Resize: New Width = New Height × (Original Width ÷ Original Height)
Simplified Ratio = (Width ÷ GCD) : (Height ÷ GCD)
Decimal Ratio = Width ÷ Height
Resize: New Height = New Width × (Original Height ÷ Original Width)
Resize: New Width = New Height × (Original Width ÷ Original Height)
Aspect Ratio Calculator
Calculate dimensions and simplify ratios.
Ratio
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Decimal
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Total Pixels
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Step-by-Step Example
Width: 1920 px
Height: 1080 px
Step 1: Find GCD of 1920 and 1080. GCD(1920, 1080) = 120.
Step 2: Divide both by GCD. 1920 ÷ 120 = 16, 1080 ÷ 120 = 9.
Simplified Ratio: 16:9
Decimal: 1920 ÷ 1080 = 1.778
Total Pixels: 1920 × 1080 = 2,073,600 (approximately 2 megapixels).
Resize Example: To resize to width 1280, new height = 1280 × (1080 ÷ 1920) = 720 px.
Use Cases
- Video production: Ensure footage matches target formats like 16:9 (YouTube, TV), 9:16 (TikTok, Instagram Reels), or 21:9 (cinema).
- Web design: Maintain image proportions when creating responsive layouts or hero banners.
- Photography: Crop images to standard print sizes (4:3 for 8×6, 3:2 for 6×4) without distortion.
- Social media: Resize images to platform-specific dimensions while preserving the aspect ratio.
- Display shopping: Compare monitor and TV aspect ratios (16:9 vs. 21:9 ultrawide) before purchasing.
Assumptions and Limitations
- The calculator works with integer pixel dimensions. Sub-pixel values are rounded to the nearest whole number.
- The GCD simplification may produce large numbers for non-standard dimensions (e.g., 1366:768 simplifies to 683:384, not a clean ratio).
- The resize tool maintains exact mathematical proportions. Actual rendered sizes may differ due to display scaling or CSS constraints.
- Only width and height are considered. The calculator does not account for pixel aspect ratio (PAR) used in some video standards.
Frequently Asked Questions
An aspect ratio is the proportional relationship between the width and height of an image, screen, or video frame. It is expressed as two numbers separated by a colon, such as 16:9. A 16:9 ratio means for every 16 units of width, there are 9 units of height. This ratio determines the shape of the display — whether it appears wide, square, or tall.
The most common aspect ratio for video content is 16:9 (widescreen). It is the standard for HDTV, YouTube, and most streaming platforms. Other common ratios include 4:3 for older TV content and presentations, 9:16 for vertical mobile video on TikTok and Instagram Stories, 21:9 for cinematic ultrawide content, and 1:1 for square Instagram posts.
To resize without distortion, you must maintain the original aspect ratio. Enter the original width and height in this calculator, then use the Resize Tool to enter either a new width or new height. The calculator automatically computes the other dimension to keep the ratio constant, preventing any stretching or squishing.
The Greatest Common Divisor (GCD) is used to simplify the ratio to its lowest terms. For example, 1920×1080 has a GCD of 120. Dividing both by 120 gives 16:9, which is much easier to understand and communicate. Without simplification, you would have to work with the raw pixel dimensions.
1920×1080 pixels is a 16:9 aspect ratio. This resolution is commonly known as Full HD or 1080p. It has been the standard for television, computer monitors, and online video since the mid-2000s. Doubling each dimension gives 3840×2160 (4K UHD), which maintains the same 16:9 ratio.
Instagram supports several aspect ratios: 1:1 (square, 1080×1080) for feed posts, 4:5 (portrait, 1080×1350) for maximum feed visibility, 9:16 (vertical, 1080×1920) for Stories and Reels, and 1.91:1 (landscape, 1080×566) for landscape posts. The 4:5 portrait format takes up the most screen space in the feed.
Total pixels (also called the resolution) is simply width × height. For a 1920×1080 image, that is 2,073,600 pixels, or approximately 2 megapixels. This determines the total amount of image data and affects file size, print quality, and the amount of memory needed to display the image.
Pixel aspect ratio is the ratio of the width to the height of an individual pixel. Most modern displays use square pixels (PAR 1:1), but some older video standards like standard-definition NTSC use non-square pixels. This calculator assumes square pixels and does not factor in PAR adjustments.
Sources and References
- ITU-R BT.709 – HDTV Standard — International standard defining the 16:9 aspect ratio for high-definition television.
- SMPTE – Society of Motion Picture and Television Engineers — Professional body establishing standards for digital cinema aspect ratios and video formats.
- W3C CSS Images Module Level 3 – Image sizing — Web standard covering how images are sized and displayed in browsers.
- Euclidean Algorithm – Khan Academy — Educational reference for the GCD algorithm used to simplify ratios.
- Schema.org WebPage Specification — Structured data standard used for the page metadata.