Free aspect ratio calculator
This aspect ratio calculator simplifies pixel dimensions into an integer ratio, calculates a missing dimension with the ratio locked, and compares fit with fill for a new canvas.
Start with width × height in whole pixels. Try 9:16, 16:9, 1:1, or 4:5 and inspect centered cropping or blank margins. No media files are opened or uploaded.
Use the aspect ratio calculator
Results update as you type. Enter width first, then height; all values are pixels.
Reduced integer ratio · width:height
16:9
Decimal width ÷ height: ≈ 1.777778:1
Fit (contain) · centered · proportions preserved
- Ideal resized source
- ≈ 1,080 × 607.5 px
- Scale factor
- ≈ 0.5625× · downscaling
- Blank left / right
- ≈ 0 px each
- Blank top / bottom
- ≈ 656.25 px each
- Canvas area left blank
- ≈ 68.3594%
Margins are measured after resizing, in target-canvas pixels, and split equally across opposite edges. No source content is cropped. Figures are ideal geometry, displayed to at most four decimal places (scale: six); very small values use scientific notation. Fractional pixels need rounding in an editor.
Includes the ratio, any locked-size result, and the current fit/fill plan.
Planning only: no file inputs, media changes, or encoding. Geometry does not certify platform safe zones, caption placement, or upload acceptance.
How the aspect ratio calculator works
- Enter the source width and height, or select a preset. The result shows an exact reduced ratio and a decimal width-to-height ratio.
- Lock that ratio, then enter a new width or height. Review the fractional result, whole-pixel recommendation, and resulting ratio.
- Choose a target canvas and compare fit with fill. The diagram and margin figures assume centered placement.
- Copy the summary and apply the dimensions in your editor. Check the real subject, captions, and export settings before publishing.
Ratio = (width ÷ greatest common divisor) : (height ÷ greatest common divisor)
New height = new width × original height ÷ original width
For example, 1920 × 1080 is 16:9. A new width of 1000 px gives an exact height of 562.5 px. The recommended 1000 × 563 px rounds that height up and therefore approximates 16:9.
Fit, fill, and the pixels outside the frame
Fit uses the smaller of the target-to-source width and height scale factors. Fill uses the larger. Both preserve proportions: fit can leave letterboxing above and below or pillarboxing at the sides, while fill can crop edges. These match contain and cover in MDN's object-fit documentation. This tool's fill mode is cover; CSS fill can instead stretch content.
Putting 1920 × 1080 into a 1080 × 1920 canvas with fit gives a 1080 × 607.5 px image and 656.25 px of blank space at both top and bottom. Fill gives an approximately 3413.3333 × 1920 px image, cropping approximately 1166.6667 px from each side in target-canvas coordinates. Fractional figures describe ideal geometry; an editor must map them to its export pixels.
The crop percentage is the share of the resized source area outside the canvas. The blank percentage is the share of the canvas left empty. Neither measures whether a face or caption remains visible. For placement planning, try the video safe zone checker and verify the actual destination app.
Choose a canvas for the destination
The presets are example dimensions, not upload or safe-zone guarantees. YouTube documents 16:9 as its standard computer-player ratio, including 1920 × 1080, and says its player adapts to other ratios. It also advises against adding padding or black bars directly to the video. See YouTube's resolution and aspect-ratio guidance before deciding whether to bake in the blank space shown here.
This calculator uses square-pixel geometry. It does not interpret anamorphic pixel aspect ratios, rotation metadata, encoder dimension restrictions, or platform interface overlays. Scaling up also does not create additional captured detail.
Common questions
How do I calculate an aspect ratio from pixels?
Divide the width and height by their greatest common divisor. For example, 1920 × 1080 reduces to 16:9. The decimal ratio is width divided by height, approximately 1.7778 in this example. Enter dimensions from 1 to 100,000 whole pixels.
How do I calculate a missing width or height?
Enter the original dimensions and lock their ratio. Choose the dimension you know and enter its new pixel count. Height equals width × ratio height ÷ ratio width; width equals height × ratio width ÷ ratio height. The calculator shows the exact fraction and a recommendation rounded to the nearest whole pixel, with a minimum of one pixel.
Why can rounding change the ratio?
An exact scaled dimension can be fractional. Rounding it to a whole pixel can slightly change the ratio, or change it substantially at tiny sizes. The tool shows the ratio of the recommended dimensions. It does not force even-number dimensions or check an encoder's requirements.
What is the difference between fit and fill?
Fit preserves the entire source inside the target canvas and can leave blank margins. Fill preserves proportions while covering the target canvas and can crop the source edges. This calculator assumes centered placement and reports margins in target-canvas pixels. Its fill mode means cover, not stretching.
Does this resize, crop, upload, or export my video?
No. This tool accepts numbers only and calculates geometry in your browser. The preview is a diagram. It does not open media files, encode an export, or certify platform safe zones or upload acceptance.
Take the plan into your edit
For supplied talking-head tutorials, UGC, founder-led recordings, and testimonials, BlitzCut offers transcript editing, adjustable silence removal, a timeline, images and audio, and captions. It is an installed app for iPhone, iPad, and Mac, with a free download and paid features; see its App Store listing and version history. Use the actual recording to judge framing and caption placement.
- How to change video aspect ratio — compare cropping and padding.
- Crop video in BlitzCut — reframe supplied footage.
- Video safe zone checker — inspect illustrative interface overlays.
- Download BlitzCut for iPhone, iPad, or Mac.
Official documentation checked October 21, 2026: MDN object-fit, YouTube aspect ratios, and the BlitzCut App Store listing.