Skip to content

Aspect Ratio Calculator

Pick a ratio, enter one dimension. The other fills in instantly.

:
px
px
Simplified ratio
16:9
1920×1080 px

How the Aspect Ratio Calculator Works

Aspect ratio expresses the proportional relationship between width and height. The formula is simple: Width = Height × (W/H), or Height = Width ÷ (W/H). Pick a preset ratio (16:9, 4:3, etc.) or enter a custom ratio, then type either dimension and the other auto-fills.

  • Lock ratio — enable to keep proportions when typing either dimension.
  • Custom ratio — type any W:H values, including decimals like 2.39:1 for cinemascope.
  • Common sizes — click a preset to instantly populate both dimensions (1920×1080, 4K, etc.).

Common Use Cases

Video production is the most common scenario. You're exporting a clip and the editor asks for a 1280×720 master, but your social team needs a 1:1 square crop and a 9:16 portrait for Reels. This tool tells you exactly how many pixels to crop from each edge, and what resolution to export to if you want to maintain sharpness at the target size.

Web design is the second major use. An OG image (Open Graph) should be 1200×630 — that's the 1.91:1 ratio used by Facebook, LinkedIn, and Twitter card previews. Banner images, hero backgrounds, and thumbnail containers all have specific ratios that must be respected to avoid unexpected cropping on different screens.

Photography has its own standards: full-frame sensors produce 3:2 images (as in 35mm film), which is why a standard 4×6 print fits perfectly. Point-and-shoot cameras typically shoot 4:3. When you order prints, selecting the wrong ratio means the lab will crop your image automatically — sometimes cutting off heads or feet.

Common sizes and copy buttons

The calculator ships with the seven ratios you'll use 90% of the time — 16:9, 4:3, 3:2, 1:1, 21:9, 9:16, and 2.39:1 cinemascope. Seven common output sizes are clickable: FHD, HD, 4K, Portrait Reel, QHD, Square, and OG image. Click any size to fill both fields at once. Copy individual values with the copy buttons — useful when pasting into Figma, Premiere, or Photoshop.

What isn't here: pixel density (PPI/DPI) conversion, crop preview graphics, or a scale factor slider. Those add enough complexity that they'd belong in a separate tool. This one stays focused on the single question you actually have: given this ratio and this width, what's the height?

Frequently Asked Questions

What is aspect ratio?
Aspect ratio is the proportional relationship between width and height, expressed as two numbers separated by a colon (e.g., 16:9). A 1920×1080 image and a 1280×720 image both have a 16:9 ratio, the ratio stays the same when you scale while keeping proportions.
What's the difference between 16:9 and 4:3?
16:9 is the standard widescreen format used by modern TVs, YouTube, and most video content. 4:3 was the standard for older TVs and computer monitors — it's squarer. The main practical difference: displaying 4:3 content on a 16:9 screen shows letterbox bars on the sides (pillarboxing), and 16:9 on 4:3 shows bars top and bottom (letterboxing).
What is 2.39:1 used for?
2.39:1 (often called anamorphic or Scope) is used in theatrical films for an ultra-widescreen cinematic look. Many major films — from Lawrence of Arabia to modern blockbusters — are shot in this format. Streaming services often preserve it, which is why you see black bars even on a widescreen TV.
What aspect ratio should I use for Instagram Reels?
Instagram Reels recommend a 9:16 aspect ratio at 1080×1920 pixels. This fills the full phone screen vertically. For a feed post, a 4:5 (1080×1350) or 1:1 square works well. Using the wrong ratio means Instagram may crop or add padding automatically.
How do I calculate the height from a width and ratio?
Height = Width ÷ (ratio W/H). For example, for a 16:9 ratio with width 1280: Height = 1280 ÷ (16/9) = 1280 × (9/16) = 720. Or just enter the width in this calculator and it fills in the height instantly.
What is the difference between 16:9 and 21:9?
16:9 (1.78:1) is the standard widescreen format used for most TVs, monitors, and video. 21:9 (approximately 2.35:1) is a wider cinematic format used in ultra-wide monitors and movies. 21:9 matches the aspect ratio of standard cinema projection, eliminating the black letterbox bars when playing movies.
Why does 9:16 matter for mobile content?
9:16 is the portrait orientation of smartphones, the inverse of 16:9. Instagram Reels, TikTok, and YouTube Shorts all use 9:16 (1080×1920 pixels). Designing content in 9:16 from the start avoids cropping issues when publishing to vertical-first platforms.
How do I maintain aspect ratio when resizing?
Multiply both dimensions by the same scale factor. For example, to scale a 1920×1080 video to half size: 1920 × 0.5 = 960 and 1080 × 0.5 = 540. Alternatively, if you know the new width, calculate the new height as: new height = new width × (original height ÷ original width). For 16:9, the multiplier is 9 ÷ 16 = 0.5625.
What aspect ratio should I use for YouTube thumbnails?
YouTube recommends 16:9 at 1280×720 pixels (minimum) or 1920×1080 pixels (full HD). The file must be under 2 MB (JPEG, PNG, or GIF). If you upload a thumbnail that isn't 16:9, YouTube adds black bars to fit the space — always use 16:9 for the cleanest result.

Common Aspect Ratios and Their Uses

  • 16:9 (1.78:1), the global standard for HD and UHD video. Used by YouTube, Netflix, broadcast TV, and most laptop/desktop monitors. Common resolutions: 1920×1080 (Full HD) and 3840×2160 (4K UHD).
  • 4:3 (1.33:1), the pre-widescreen TV and early computer monitor standard. Still used in some educational video content and iPad displays.
  • 21:9 (2.33:1 ultrawide) — used in cinema and ultrawide monitors. Cinematic widescreen films are often delivered at 2.39:1 on Blu-ray, which is why you see black bars on a standard 16:9 screen.
  • 1:1 — square format. Used for Instagram grid posts, some social media profile images, and album artwork.
  • 9:16 — vertical video. The default smartphone orientation. Used by Instagram Reels, TikTok, and YouTube Shorts at 1080×1920 pixels.
  • 3:2, the standard DSLR and mirrorless camera sensor ratio, originating from the 35mm film frame. Most full-frame cameras default to 3:2. A standard 4×6" print is 3:2.
  • 4:5, the Instagram portrait photo format. At 1080×1350 pixels, it takes up more screen space in the feed than a square post, making it the optimal ratio for engagement on mobile.

Related tools: Color Picker, Color Contrast Checker, and Percentage Calculator.

When You Need an Aspect Ratio Calculator

  • Resizing video for different platforms — avoid stretching or adding unwanted black bars (pillarboxing or letterboxing) when adapting a master video to multiple output formats.
  • Embedding video on a webpage — calculate the correct height for a given container width to maintain 16:9 without layout shift (e.g., container is 800px wide → height = 800 × 9/16 = 450px).
  • Cropping photos for print — 4×6" = 3:2, 5×7" ≈ 5:7, 8×10" = 4:5. Each print size has a specific ratio; knowing it in advance prevents the lab from auto-cropping your image unexpectedly.
  • Responsive CSS padding trick — before the CSS aspect-ratio property was broadly supported, developers used a padding-top percentage equal to height/width × 100 to create ratio-preserving boxes (e.g., 56.25% for 16:9).
  • Social media thumbnail sizing — each platform has recommended dimensions with specific ratios: YouTube thumbnails (16:9, 1280×720), Facebook link previews (1.91:1, 1200×630), LinkedIn posts (1.91:1 or 1:1).
  • Architecture and scale drawings — maintaining ratio while scaling a floor plan or diagram up or down ensures that proportions remain accurate across different print sizes and presentation formats.

By Bam's Thinkery — Updated