Use this tool’s Dimension units selector. Centimeters, millimeters and inches convert each other; pixels need a separate DPI assumption and are not converted to print sizes.
How to use this aspect ratio calculator
Choose your task and units. Resize starts with the original width and height; crop and pad keep the original image scale and change its frame. No upload is needed.
How the calculation works
For crop, fit the largest rectangle of the target ratio inside the original; for pad, fit the smallest rectangle around it. At 1440 × 1080 to 16:9, crop is 1440 × 810 (135 removed at top and bottom, 75% retained). Pad is 1920 × 1080 (240 added left and right). Closest-standard error is the relative difference between the exact width/height quotient and a preset; it never changes your dimensions.
An aspect ratio is width:height. A 1,920 × 1,080 image reduces to 16:9 after dividing both dimensions by their greatest common divisor, 120.
For a ratio W:H and known height h, width = h × W ÷ H. For a known width w, height = w × H ÷ W. These operations preserve the image’s proportions before pixel rounding.
Pixels need whole numbers: resize rounds to nearest, crop inward and pad outward, with a minimum of 1. The breakdown also offers a nearby exact-ratio pixel size, which may change both dimensions. Physical dimensions keep fractional values. Displayed decimals may be shortened.
Identify and resize use the original dimensions directly. A 4032 × 3024 image resized to width 1200 becomes 1200 × 900. Custom ratios accept decimals such as 2.35:1, reduced to 47:20.
Worked example
At 16:9, a height of 720 px gives a width of 720 × 16 ÷ 9 = 1,280 px. At 4:3, a width of 1,000 px gives a height of 750 px. Entering 1,080 × 1,920 in Identify mode returns 9:16.
Limits and assumptions
Plans dimensions for square-pixel images or matching physical units. Crop and pad are centered geometric plans, not image-editing operations. No upload, image export, print DPI or non-square video pixels. Pixel rounding may slightly change the ratio; odd edge differences need one extra pixel on one side.
Frequently asked questions
Can I enter 2.35:1 or resize from an existing photo?
Yes. Custom ratios accept decimals. Resize original → new width/height keeps your original proportions and derives the other side automatically; no ratio needs to be copied.
How do I calculate a 16:9 resolution?
Choose 16:9 and enter one known dimension. With a height of 1,080, the width is 1,920 pixels.
Can I calculate portrait sizes?
Yes. Choose 9:16 or 4:5, or enter a custom width:height ratio. The preview changes to the corresponding shape.
Why is the calculated dimension rounded?
Images need whole pixels. For awkward sizes, check the unrounded value and nearby exact-ratio dimensions in the breakdown.
Will this resize my actual image?
It calculates dimensions. Apply those dimensions in your image editor; no image is uploaded or changed here.