Images & photos · Social Image Resizer
4:5, 0.8 or 1600×2000: Three Ways to Write the Same Aspect Ratio
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A ratio like 4:5, a decimal like 0.8 and a pixel size like 1600×2000 all describe the same shape, and specs mix them freely. This post explains how to convert between them, how to reduce a dimension pair to its simplest ratio, and where rounding creates confusion.
Three specs, one shape — the concrete confusion when one source says 4:5, another 0.8 and a third gives pixels
A brief can describe one portrait shape as 4:5, 0.8 or 1600×2000. The first is a proportion, the second is width divided by height, and the third is one concrete pixel grid with that proportion. Confusing these forms can rotate a crop or produce dimensions that are merely close to the intended shape.
Social Image Resizer accepts familiar ratio choices and custom text such as `4:5`, `4/5` or `1.91:1`. Its parser returns width divided by height, then sizeFromRatio combines that number with a longest-edge budget to produce integer dimensions. The arithmetic is visible and unit-tested.
Ratio notation — width to height, why order matters, and why 5:4 and 4:5 are different orientations of the same numbers
Ratio order is width first, height second. Four to five means a portrait because four units of width occupy less than five units of height. Five to four is landscape. The same two numbers do not describe the same orientation once their order is reversed.
Ratios can be scaled without changing shape: 4×5, 800×1000 and 1600×2000 all reduce to the same relation. They do not contain a resolution by themselves. A ratio tells the cropper the rectangle’s shape; a pixel pair tells the renderer how many samples the final rectangle contains.
Decimal form — dividing width by height, and why decimals like 1.78 are approximations of 16:9
Decimal form comes from division. Four divided by five is exactly 0.8, while sixteen divided by nine repeats and is commonly rounded in prose. A decimal like 1.78 may therefore be a shorthand rather than an exact replacement for 16:9. Using the original fraction avoids unnecessary drift.
ToolAcre’s custom parser supports decimal terms on either side of the colon, which is why `1.91:1` is valid. It rejects zero and malformed text. The resulting JavaScript number still participates in rounded integer output dimensions, so retain the requested notation when exact provenance matters.
From pixels to a ratio — reducing a dimension pair by its greatest common divisor, and why 'almost 4:5' happens
To reduce pixel dimensions to a simple integer ratio, divide width and height by their greatest common divisor. For 1600×2000, the divisor is 400, leaving 4×5. If a pair does not reduce to the expected ratio, compare its decimal width divided by height and decide whether rounding created the difference.
Not every useful ratio has a neat small-integer reduction after output rounding. sizeFromRatio rounds the calculated shorter edge, so a custom longest edge can produce a pair that approximates the requested decimal. The canvas still needs positive integer width and height; fractional output pixels do not exist.
Worked example: reducing a few dimension pairs — the arithmetic, and spotting when a pair is not quite the ratio it claims
Reduce 1080×1350 by their greatest common divisor, 270, to obtain 4:5. Divide 1200 by 630 to obtain about 1.9048, which the current Open Graph preset labels 1.91:1 as a concise description. Divide 1584 by 396 and obtain exactly 4, matching the current 4:1 LinkedIn-labelled banner preset.
These examples describe present ToolAcre presets, not permanent destination specifications. Their value here is arithmetic. A reviewer can detect when a dimension pair matches its label exactly, when it is a rounded convention and when someone has accidentally swapped orientation.
Orientation words — portrait, landscape, square, vertical and how they map onto the numbers
Square means width equals height. Portrait means width is smaller; landscape means width is larger. “Vertical” often describes a tall portrait such as 9:16, but words are less precise than numbers. Always retain the ordered ratio or dimension pair in production notes.
ToolAcre’s current labels distinguish Square 1:1, Portrait 4:5, Full portrait 9:16 and Landscape 16:9. Those words help navigation, while the values drive geometry. If a stakeholder says only “portrait,” ask for the ratio or destination instead of guessing between several tall shapes.
What this does not cover — which platform uses which ratio today; treat the numbers here as arithmetic examples, not specs
This article does not assign today’s ratios to social products beyond the dated preset table. Platforms can revise dimensions and presentations. Arithmetic remains valid, but whether a destination wants 4:5 today is an external current-state question that must be checked against its own guidance.
It also does not claim that two equal-ratio files have equal quality. A 400×500 image and 1600×2000 image share shape but not pixel count. Source detail, scaling direction, encoding and display size remain separate variables that ratio notation alone cannot answer.
Takeaway: convert with confidence — the Social Image Resizer lets you pick the aspect ratio a platform expects and handles the pixel arithmetic
Translate notation by keeping the concepts separate: ratio for shape, decimal for numerical comparison and dimensions for the concrete pixel grid. Use greatest-common-divisor reduction when integer pairs permit it, and expect rounding when a ratio meets an integer longest edge.
Social Image Resizer performs that last conversion for custom ratios and publishes the actual output dimensions. Check the calculated pair, preserve the intended ratio in review notes and confirm the destination’s current requirement. That replaces notation confusion with inspectable arithmetic.