How to use
Use this calculator when preparing dimensions for an image, video frame or layout placeholder. Start with the original width and height, then choose whether the new width or new height is fixed. Enter the target value for that one side and calculate. The other side follows automatically from the original proportions.
Use one consistent unit: pixels for digital dimensions, or the same abstract unit for all three numbers. A ratio has no physical unit. A width of 16 and height of 9 has the same shape as 1920 by 1080. This page does not need an image file.
The pale examples calculate without editing. Focusing any numeric field clears all examples together; later edits keep your own values. The compact diagram stays visible when values are missing or invalid. Dimension labels update with valid values; a dash means the dimension is not yet available.
How the result is calculated
For original width W and height H, the ratio is W:H. Integer inputs are reduced by their greatest common divisor; decimal dimensions use the approximate width/height ratio instead. If you fix the new width N, the new height is N × H / W. If you fix the height N, the new width is N × W / H.
The scale is new size divided by original size on the selected side. Both rectangles use the same drawing scale, so a smaller result occupies less space. Long or very thin rectangles can be hard to see; their adjacent dimension labels remain the authoritative values. The illustration is not a measurement of your screen.
Two worked examples
A 1920 × 1080 frame has a 16:9 ratio. Choosing a new width of 1280 gives a height of 720 and a scale of about 0.67. This plans a smaller frame without changing its shape.
For a portrait image of 1200 × 1800, set the new height to 900. The width becomes 600, the scale is 0.5 and the ratio remains 2:3. A square such as 800 × 800 always remains 1:1.
Input and output limits
Every input must be greater than zero and no more than one billion. A decimal point or comma is accepted, without thousands separators. Results above one trillion are rejected. The display normally rounds to two decimal places while calculations retain precision; a tiny positive value is shown as less than 0.01 rather than zero.
Use Copy result to take the original dimensions, ratio, scale and new dimensions into your editing notes. Editing any input or selection clears the confirmed result and disables copying until you calculate again. Clear removes numeric inputs and keeps the empty diagram while preserving the selected target side.
Can I enter both target dimensions?
Only one target side is fixed. If an external template specifies both sides and has a different ratio, preserving the complete image requires a separate choice about cropping or padding. This calculator makes neither decision silently.
Does this resize my image?
No. It calculates dimensions only; it does not upload, crop, resample or export an image. Apply the dimensions in an image editor.
What if I need whole pixels?
A proportional dimension may be fractional. Rounding it to a whole pixel can change the ratio slightly. The result preserves the mathematical ratio rather than promising an exact integer raster.
Does a matching ratio mean matching screen size?
No. Equal ratios describe shape, not physical width or diagonal size. Screen measurements and pixel density are separate tasks.