--- url: https://findutils.com/guides/aspect-ratio-calculator-guide title: "Aspect Ratio Calculator: Resize Without Stretching" description: "Find the aspect ratio of any width and height, then get the matching new size with the free FindUtils Aspect Ratio Calculator. Video, photo and CSS examples." category: design content_type: guide guide_type: subtopic cluster: design locale: en read_time: 9 status: published author: "olgunozoktas" published_at: 2026-10-19T15:08:00Z excerpt: "Type a width and a height, read the simplified ratio, then enter the new width you need and get the height that keeps the picture in proportion. This guide covers the math, why many 16:9 screens are not exactly 16:9, how to change a ratio by cropping, and the rounding mistakes that break video exports." tag_ids: ["design", "aspect-ratio", "image-resizing", "video", "responsive-design"] tags: ["Design", "Aspect Ratio", "Image Resizing", "Video", "Responsive Design"] primary_keyword: "aspect ratio calculator" secondary_keywords: ["resize without stretching", "calculate height from width aspect ratio", "16:9 resolution calculator", "what is 1366x768 aspect ratio", "css aspect-ratio", "4:5 instagram size"] tool_tag: "aspect-ratio-calculator" related_tool: "aspect-ratio-calculator" related_tools: ["aspect-ratio-calculator", "image-resizer", "image-cropper", "video-resizer", "video-cropper", "placeholder-image-generator", "screen-resolution-detector", "gcd-lcm-calculator"] updated_at: "2026-10-19T15:08:00Z" og_image: "/images/content/guides/aspect-ratio-calculator-guide-cover-20261019.webp" image_alt: "Three nested picture frames of different sizes share one dashed diagonal line from corner to corner, next to a tall phone-shaped frame and a small square." --- An aspect ratio calculator tells you the shape of a picture and keeps that shape when you change its size. Type the original width and height into the FindUtils [Aspect Ratio Calculator](/calculate/aspect-ratio-calculator/), and it reduces them to a ratio such as 16:9. Then type the new width you need, and it returns the height that keeps the image from stretching: 1920 × 1080 at a width of 1280 becomes 1280 × 720. It is free, needs no signup, and works in your browser. This guide explains what the numbers mean, walks through each field of the tool, and covers four everyday jobs: exporting video, resizing photos, reserving space for images on a web page, and sizing posts for social apps. It also covers why many "16:9" screens are not exactly 16:9 and the rounding mistakes that break video exports. ## What Is an Aspect Ratio? An aspect ratio is the width of a picture divided by its height, written as two whole numbers with a colon. A 1920 × 1080 image is 16:9 because both sides divide by their greatest common divisor, 120: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9. The calculator does exactly this, so the ratio it shows is always the fully reduced one. (The same divisor is what the [GCD & LCM Calculator](/calculate/gcd-lcm-calculator/) finds.) The ratio describes shape, not size. 1280 × 720, 1920 × 1080 and 3840 × 2160 are all 16:9: they have the same shape at three different sizes. Scale an image so that both sides change by the same factor and the ratio stays the same. Change only one side and the picture stretches. The calculator has nine one-click presets. Here is what each one means as a decimal (width ÷ height) and where you usually meet it: | Ratio | Width ÷ height | Shape | Common use | |-------|----------------|-------|------------| | 16:9 | 1.7778 | Landscape | HD and 4K video, YouTube, most TVs | | 4:3 | 1.3333 | Landscape | Older TVs and monitors, many phone camera photos | | 21:9 | 2.3333 | Wide landscape | Ultrawide monitors (a marketing name, see below) | | 1:1 | 1.0000 | Square | Profile pictures, square posts | | 4:5 | 0.8000 | Portrait | Portrait feed posts | | 9:16 | 0.5625 | Tall portrait | Stories, Reels, Shorts, phone screens | | 3:2 | 1.5000 | Landscape | Photos from many DSLR and mirrorless cameras | | 5:4 | 1.2500 | Landscape | Older 1280 × 1024 monitors | | 2:3 | 0.6667 | Portrait | Portrait prints such as 4 × 6 inches | A ratio above 1 is landscape, exactly 1 is square, and below 1 is portrait. ## How to Use the Aspect Ratio Calculator ### Step 1: Enter the Original Width and Height Open the [Aspect Ratio Calculator](/calculate/aspect-ratio-calculator/) and type the width and height of your image, video or screen in pixels under Original Dimensions. The fields take whole numbers. If you only know the target shape and not a size, click one of the Common Ratios presets instead: it fills in the ratio itself, for example 16 and 9. ### Step 2: Read the Ratio and the Decimal The Aspect Ratio panel shows the reduced ratio, such as 16:9, with the decimal under it: 1.7778 (177.78%). The decimal is width divided by height. A dashed preview box draws the shape so you can see at a glance whether it is landscape, square or portrait. ### Step 3: Type a New Width or Height In the Resize Calculator, type the width you need into New Width. The calculator fills in New Height so the shape stays the same. If the height is the fixed side, for example a 1080-pixel-tall video, type into New Height and the width is calculated instead. The field you typed in last is the one that stays fixed, and it is highlighted. The result is rounded to the nearest whole pixel, because an image cannot have half a pixel. For 1920 × 1080 at a width of 1280, the exact height is 720, so nothing is rounded. For a width of 1000, the exact height is 562.5 and the calculator shows 563. ### Step 4: Export or Copy the Numbers Use the export button in the Aspect Ratio panel to save the result as CSV or JSON, or to print it. The export includes your original size, the reduced ratio and the decimal, which is handy when you hand sizes over to a designer or a video editor. ## Four Everyday Jobs ### Exporting a Smaller Video A 4K clip is 3840 × 2160. Enter it, type 1920 as the new width, and the height is 1080: the same 16:9 shape at a quarter of the pixels. YouTube's own [list of recommended resolutions](https://support.google.com/youtube/answer/6375112) for 16:9 runs from 7680 × 4320 down to 426 × 240, and you can check any of them this way. Then set those numbers in the [Video Resizer](/media/video-resizer/). ### Resizing a Phone Photo Many phone cameras save 4032 × 3024 photos. The calculator shows 4:3. To fit a 1600-pixel-wide space on a blog, type 1600 and you get 1200. The [Image Resizer](/convert/image-resizer/) can then make the smaller copy, and the [resize images guide](/guides/how-to-resize-images-online/) covers quality settings. ### Reserving Space for Images on a Web Page A page jumps when images load without a known size, which hurts the Cumulative Layout Shift score. web.dev's [guide to optimizing CLS](https://web.dev/articles/optimize-cls) recommends always setting `width` and `height` on images and videos, or reserving the space with the CSS `aspect-ratio` property. Browsers use the two attributes to work out the ratio before the file arrives: ```html Product on a desk ``` ```css .video-frame { width: 100%; aspect-ratio: 16 / 9; } ``` [MDN](https://developer.mozilla.org/en-US/docs/Web/CSS/aspect-ratio) notes that `aspect-ratio` only takes effect when at least one of the box's sizes is automatic, and that the property has been available across browsers since September 2021. You can paste the ratio from the calculator straight into it: `16 / 9`, `4 / 5` and so on. ### Sizing Social Posts Instagram's help page on [photo resolution](https://help.instagram.com/1631821640426723) says feed photos keep their resolution between 1.91:1 and 3:4, which at 1080 pixels wide means a height between 566 and 1440 pixels. Click the 4:5 preset and type 1080 as the new width: the height is 1350, inside that range. For a 9:16 story at the same width, the height is 1920. The 1200 × 630 size often used for link preview images reduces to 40:21, a decimal of about 1.905, which is why it is usually described as 1.91:1. The [Open Graph tags post](/blog/open-graph-tags-explained-why-link-previews-look-wrong/) explains how those previews are built. ## Why Some "16:9" Screens Are Not Exactly 16:9 The calculator never rounds a ratio to the nearest familiar name, so some well-known sizes show surprising results: | Resolution | Calculator shows | Decimal | Usually sold as | |------------|------------------|---------|-----------------| | 1920 × 1080 | 16:9 | 1.7778 | 16:9 | | 1366 × 768 | 683:384 | 1.7786 | 16:9 | | 854 × 480 | 427:240 | 1.7792 | 16:9 (480p) | | 1440 × 900 | 8:5 | 1.6000 | 16:10 | | 2560 × 1080 | 64:27 | 2.3704 | 21:9 | | 3440 × 1440 | 43:18 | 2.3889 | 21:9 | 1366 × 768 is close to 16:9 but not exact: 768 × 16 ÷ 9 is 1365.33, which was rounded up to a whole pixel. 854 × 480 has the same story, since 480 × 16 ÷ 9 is 853.33. "21:9" is a marketing name: 21 ÷ 9 is 2.3333, but the common ultrawide sizes are 2.37 and 2.39. When the ratio looks strange, compare the decimals. Two sizes whose decimals agree to two places look the same to the eye. To check the screen you are using right now, the [Screen Resolution Detector](/network/screen-resolution-detector/) shows its resolution, viewport and device pixel ratio. ## Changing the Ratio: Crop or Pad, Never Stretch The calculator keeps a shape. It cannot turn a landscape video into a vertical one without losing something, and no tool can. To change the ratio you have two honest choices: - **Crop**: cut away part of the picture. To turn a 1920 × 1080 clip into 9:16, keep the full height of 1080 and cut the width to 1080 × 9 ÷ 16 = 607.5, so 608 pixels. Use the [Video Cropper](/media/video-cropper/) for clips and the [Image Cropper](/design/image-cropper/) for photos; the [image cropper guide](/guides/image-cropper-guide/) shows how to lock a crop to a ratio. - **Pad**: keep the whole picture and add bars or a background around it. YouTube's help page advises against adding bars to the video itself, because its player already adapts to the video's shape. Changing only the width or only the height is the third option, and it is the one that makes faces look wide or thin. ## Ways to Get Proportional Sizes Compared | Method | Finds the reduced ratio | Calculates the other side | Shows odd ratios honestly | Cost | |--------|------------------------|---------------------------|---------------------------|------| | FindUtils Aspect Ratio Calculator | Yes | Yes, width or height | Yes (683:384, 64:27) | Free, no signup | | Math by hand | With a GCD step | Yes: new height = new width × height ÷ width | Yes | Free, slower | | "Constrain proportions" in an image editor | Usually not shown | Yes | Not shown | Often paid software | | CSS `aspect-ratio` | No, you supply it | In the browser, at layout time | Not applicable | Free | Image editors are the right place to do the actual resize. The calculator is useful before that, when you plan sizes for several outputs at once or need to explain a size to someone else. ## Common Mistakes to Avoid ### Mistake 1: Ending Up With Odd Pixel Sizes for Video Many video encoders expect even widths and heights, so a calculated 563 can make an export fail or get silently changed. Round to the nearest even number yourself, or let the encoder do it. In FFmpeg, the [scale filter](https://ffmpeg.org/ffmpeg-filters.html#scale) accepts `-2` for one side: it keeps the aspect ratio and makes that side divisible by 2, for example `scale=1280:-2`. ### Mistake 2: Using the Decimal Upside Down The calculator's decimal is width ÷ height: 1.7778 for 16:9. The older CSS "padding-top" trick for responsive boxes needs height ÷ width instead, which is 9 ÷ 16 = 56.25%. If you write 177.78% there, the box comes out far too tall. Modern CSS avoids the problem: `aspect-ratio: 16 / 9` reads in the same order as the ratio. ### Mistake 3: Scaling Up Past the Original The calculator will happily give you 3840 × 2160 for a 1280 × 720 source. The shape is right, but the extra pixels are invented and the result looks soft. Scale down when you can, and start from the largest original when you need several sizes. ### Mistake 4: Typing Decimal Ratios The fields take whole pixels, so a ratio such as 2.39:1 cannot be typed directly. Multiply both sides by 100 and enter 239 and 100: the calculator shows 239:100 with the decimal 2.39, and the resize fields work as usual. ### Mistake 5: Expecting the Calculator to Edit the File The calculator only does the math. Nothing is uploaded, and no file changes until you apply the numbers in an editor or one of the resize and crop tools below. To try a layout before the real image exists, the [Placeholder Image Generator](/generate/placeholder-image-generator/) makes a test image at exactly the size you calculated. ## Tools Used in This Guide - **[Aspect Ratio Calculator](/calculate/aspect-ratio-calculator/)**: Reduce any width and height to a ratio and calculate proportional sizes - **[Image Resizer](/convert/image-resizer/)**: Make a smaller copy of a photo at the size you calculated - **[Image Cropper](/design/image-cropper/)**: Cut a photo to a new ratio - **[Video Resizer](/media/video-resizer/)**: Change a video's resolution - **[Video Cropper](/media/video-cropper/)**: Crop a landscape clip to vertical or square - **[Placeholder Image Generator](/generate/placeholder-image-generator/)**: Create a test image at an exact size - **[Screen Resolution Detector](/network/screen-resolution-detector/)**: See the resolution and pixel ratio of your screen - **[GCD & LCM Calculator](/calculate/gcd-lcm-calculator/)**: Find the greatest common divisor behind a reduced ratio ## FAQ ### How do I calculate the height from the width and an aspect ratio? Multiply the new width by the original height and divide by the original width. For 16:9 at a width of 1280, that is 1280 × 9 ÷ 16 = 720. The Aspect Ratio Calculator does this as you type and rounds to the nearest whole pixel. ### What aspect ratio is 1366 × 768? Exactly, it is 683:384, with a decimal of 1.7786. That is close enough to 16:9 (1.7778) that it is sold as a 16:9 screen, but it is not an exact match because 768 × 16 ÷ 9 is not a whole number. ### What aspect ratio is 1920 × 1080? 16:9. Both sides divide by 120, giving 16 and 9. 1280 × 720, 2560 × 1440 and 3840 × 2160 have the same ratio. ### Is 21:9 really 21 to 9? Not usually. 21 ÷ 9 is 2.33, but the common ultrawide resolutions are 2560 × 1080 (64:27, about 2.37) and 3440 × 1440 (43:18, about 2.39). "21:9" is a convenient label for that family of wide screens. ### How do I change a video from 16:9 to 9:16 without stretching it? Crop it. Keep the height and cut the width to height × 9 ÷ 16, for example 608 pixels wide for a 1080-pixel-tall clip, then position the crop over the part that matters. Changing only one dimension stretches the picture. ### Is the aspect ratio calculator free? Yes. The FindUtils Aspect Ratio Calculator is free, needs no account, and has no usage limits. It only works with the numbers you type; no image is uploaded. ### What is the best aspect ratio for Instagram? For feed photos, Instagram keeps any ratio between 1.91:1 (landscape) and 3:4 (portrait) at up to 1080 pixels wide. Portrait 4:5 at 1080 × 1350 is a popular choice because it fits that range while taking up more of the screen than a square; stories use 9:16. ## Next Steps - Shrink photos to the size you calculated with the [guide to resizing images online](/guides/how-to-resize-images-online/). - Lock a crop to a ratio in the [image cropper guide](/guides/image-cropper-guide/). - Change a clip's resolution step by step in the [video resizer guide](/guides/video-resizer-guide/). - Find every image tool in the [complete guide to online image tools](/guides/complete-guide-to-online-image-tools/). ## Sources - [MDN: aspect-ratio CSS property](https://developer.mozilla.org/en-US/docs/Web/CSS/aspect-ratio) - [web.dev: Optimize Cumulative Layout Shift](https://web.dev/articles/optimize-cls) - [YouTube Help: Video resolution and aspect ratios](https://support.google.com/youtube/answer/6375112) - [Instagram Help Center: Image resolution of photos you share on Instagram](https://help.instagram.com/1631821640426723) - [FFmpeg Filters Documentation: scale](https://ffmpeg.org/ffmpeg-filters.html#scale)