Aspect Ratio Calculator
Determine the aspect ratio of an image, video, or screen from its width and height. You can also enter a known aspect ratio and one dimension to calculate the other. Useful for responsive design, video editing, and display resolution planning.
Aspect ratio is the relationship between the width and height of a visual frame, written as two numbers separated by a colon (16:9, 4:3, 1:1). It's the single most important measurement when working with images, video, or screens — because every device, platform, and codec has opinions about what aspect ratios it shows correctly. Upload a 16:9 video to Instagram Reels and the platform will crop, letterbox, or stretch it; design a banner at 1.91:1 for Facebook and it'll look right everywhere. Get the ratio wrong and your content gets distorted or cut off.
The math is simple: divide the width and height by their greatest common divisor (GCD). For 1920×1080, the GCD is 120, so the ratio simplifies to 16:9. The calculator handles this automatically, plus the more common practical use case: given one dimension and a target aspect ratio, find the other. That's how you resize for a social media spec, plan a poster print, or scale a video thumbnail without distortion.
This page covers ratio math, the standard ratios you'll meet in practice (cinema, broadcast, web, social, mobile), how aspect ratio interacts with pixel density and resolution, and how to avoid the cropping pitfalls that wreck content on platforms with unusual specs.
Inputs
Results
Aspect Ratio
16:9
Decimal
1.7778
Megapixels
2.07 MP
Orientation
Landscape
Resolution Details
| Detail | Value |
|---|---|
| Width | 1,920 px |
| Height | 1,080 px |
| Aspect Ratio | 16:9 |
| Decimal Ratio | 1.7778 |
| Common Name | Widescreen (16:9) |
| Orientation | Landscape |
| Total Pixels | 2,073,600 |
| Megapixels | 2.07 MP |
Formula
How to use this calculator
- Enter the width and height of your image, video, or screen in pixels.
- Read the simplified ratio (e.g., 16:9) and the decimal value (1.778).
- For resizing: figure out which dimension is fixed (e.g., target width = 1080 for Instagram), then compute the matching dimension from the desired ratio.
- Cross-check against platform specs — sites like YouTube, Instagram, and TikTok publish exact aspect ratio requirements.
- For print: aspect ratios for standard paper sizes (Letter, A4) and photo prints (4×6, 5×7, 8×10) are not all equal; check before printing.
- For video: confirm both display ratio and pixel aspect ratio (PAR). Some legacy formats use non-square pixels (DV, SD broadcast).
Worked examples
YouTube thumbnail dimensions
**Scenario:** You're creating a YouTube video thumbnail. YouTube recommends 1280×720 pixels. **Calculation:** Ratio: 1280:720, GCD = 160, simplifies to 8:9 — wait, that's wrong direction. 1280÷160 = 8, 720÷160 = 4.5. Recompute: GCD(1280, 720) = 80. 1280÷80 = 16, 720÷80 = 9. Ratio = 16:9. **Result:** YouTube thumbnails are 16:9 at 1280×720. You can deliver larger sizes (1920×1080, 3840×2160) as long as the ratio stays 16:9 — YouTube resizes automatically. Maximum file size is 2 MB and YouTube prefers JPG, PNG, or GIF.
Cropping a photo for Instagram portrait
**Scenario:** You have a DSLR photo at 6000×4000 (3:2 ratio) and want to post it as Instagram portrait (4:5, recommended 1080×1350). **Calculation:** Original 3:2 = 1.5 decimal. Target 4:5 = 0.8 decimal. You need to either crop height (would need 6000×7500 — impossible without adding pixels) or crop width. Crop width: at 4000 height, width = 4000 × (4/5) = 3200. Crop the 6000-wide image down to 3200×4000, then resize to 1080×1350. **Result:** Crop 6000×4000 down to 3200×4000 (removing 1400px width, centered or composed), then resize to 1080×1350 for upload. Cropping costs you ~47% of the original image area, so frame the shot accordingly.
Choosing a monitor for video editing
**Scenario:** You're editing 16:9 video and considering a 16:10 monitor (1920×1200) vs a 21:9 ultrawide (3440×1440). **Calculation:** 16:10 at 1920 wide → 1920×1080 video fits in 1920×1080 with 120px below for timeline. 21:9 at 3440 wide → 1920×1080 video preview fits with ~1520 pixels left over (room for the entire timeline, browser, and a notes panel side by side). **Result:** For dedicated video work, 21:9 ultrawide gives much more horizontal space for the timeline and bins without scrolling. 16:10 is more efficient for general productivity (web pages, documents). 16:9 with the same diagonal is shorter and less useful for editing — most pros pick 16:10 or 21:9.
When to use this calculator
**Use aspect ratio math when you need to:**
- **Resize for a platform spec**: every social network has its own ideal ratio. Resize at upload time, not in-platform (their auto-crop is often unflattering). - **Plan responsive design**: `aspect-ratio: 16/9;` is now a first-class CSS property — much cleaner than the old padding-bottom hack. - **Choose displays and projectors**: presentation rooms often have weird ratios. 16:10 projectors are still common in offices; 16:9 dominates conference rooms. - **Mix camera and delivery formats**: shoot 3:2 stills knowing you'll crop to 4:5 or 1:1 for social. Shoot 4K 16:9 video knowing you might reformat to 9:16 for vertical platforms. - **Frame for crop-safety**: when shooting for multiple delivery ratios, keep important content in the "intersection" of all target crops — typically a centered 1:1 region.
**Aspect ratio gotchas to watch for:**
- **Stretched content**: when display PAR ≠ source PAR, video can look squished or stretched (anamorphic flag missing). - **Letterboxing vs pillarboxing**: black bars top/bottom = letterbox (wider source on narrower display); black bars left/right = pillarbox (narrower source on wider display). - **Variable ratios**: IMAX films often switch between 1.43:1 and 1.90:1 mid-scene. Streaming versions usually pick one and crop the rest. - **Mobile-first design**: most viewing is now 9:16 portrait; design for that and adapt up, not down.
Common mistakes to avoid
- Confusing aspect ratio with resolution. 720p and 4K are both 16:9 — they have the same shape but different pixel counts.
- Trying to add pixels to enlarge to a target ratio. You can only crop down or letterbox/pillarbox — you can't invent image data.
- Forgetting that some sensors use non-square pixels. Old DV camcorders had pixel aspect ratio (PAR) of 1.0926, so 720×480 was actually 16:9 display, not 3:2.
- Designing for 16:9 only and assuming social media will look right. Vertical (9:16) and square (1:1) crops often need separately composed shots.
- Cropping by gut instead of math. Use the calculator: at this height, what width matches my target ratio? Then trim precisely.
- Misreading orientation. "16:9" is landscape (wider than tall). "9:16" is portrait (taller than wide). They're inverses of each other.
- Submitting print files at the wrong ratio. 4×6 is 3:2; 5×7 is 1.4:1; 8×10 is 5:4. Each requires a different crop from a typical 3:2 photo.