🖥️ Display

Aspect Ratio Calculator

Simplify a width and height to its aspect ratio, scale it to a new width and check pixel density. Press Calculate.

Written and reviewed by SM Arijul Islam · Last reviewed 27 October 2026 · Editorial standards · Report an error

About the Aspect Ratio Calculator

An aspect ratio is the width divided by the height, reduced to whole numbers. 1920 × 1080 reduces to 16:9; 1440 × 1080 reduces to 4:3. The simplified ratio is useful for describing a display or a video frame, but the actual pixel count still matters for sharpness.

Scaling by aspect ratio keeps the shape. If 1920 × 1080 is scaled to 2560 wide, the height is 2560 × 9/16 = 1440. Pixel density (PPI) then uses the diagonal: √(w² + h²) ÷ diagonal inches. A 27-inch 1440p monitor is about 109 PPI; a 27-inch 4K monitor is about 163 PPI.

How the calculation works

Ratio = width ÷ height.
Simplified ratio = width:height after dividing by the greatest common divisor.
New height = new width ÷ ratio.
PPI = √(width² + height²) ÷ diagonal inches.

Reference values

Common display resolutions
Resolution	Ratio	PPI at 27 in
1280 × 720	16:9	54
1920 × 1080	16:9	82
2560 × 1440	16:9	109
3840 × 2160	16:9	163
3440 × 1440	21:9	110
5120 × 1440	32:9	111

Worked example: reducing and scaling a frame

A 2560 × 1080 ultrawide is 64:27, not exactly 21:9. Scaling a 1920 × 1080 frame to 1280 wide gives 720 high. A 4:3 slide at 1920 wide is 1440 high, so it needs 2.76 MP versus 2.07 MP for 16:9—a third more pixels for the same width.

The simplified ratio describes the shape, but the pixel count still matters. Two displays can share a 16:9 ratio while one is 720p and the other is 4K. Use the ratio for layout and the resolution for sharpness; neither replaces the other.

Cropping, letterboxing and pillarboxing

Fitting one ratio inside another always costs something. Letterboxing adds bars above and below to keep the full width, so a 16:9 video shown on a 4:3 screen loses height to black bars. Pillarboxing adds bars at the sides, which is what happens when 4:3 archive footage plays on a 16:9 television. Cropping fills the frame but discards part of the image, and the amount discarded grows with the mismatch: fitting 16:9 into 4:3 crops about 25% of the width, while fitting 4:3 into 16:9 crops about 25% of the height.

If the subject sits near an edge, crop from the side that matters least rather than centring blindly. For social video, keep titles and faces inside the middle 80% of the frame so a later crop to a square or vertical format does not cut them off.

Frequently asked questions

What is the difference between 16:9 and 16:10?

16:9 is 1.778 width-to-height; 16:10 is 1.6. A 16:10 screen is taller for the same width, which suits documents and code.

Does a higher PPI always look better?

Up to a point. Beyond about 200 PPI at normal viewing distance, the benefit is marginal without scaling. Colour, contrast and coating matter more.

How do I scale a video without distortion?

Multiply both dimensions by the same factor, or use the ratio to compute one dimension from the other. Cropping changes the ratio; letterboxing preserves it.

Is 21:9 the same as 64:27?

Not exactly. 21:9 is a marketing label. A 2560 × 1080 screen is 64:27 (2.37:1), while 3440 × 1440 is 43:18 (2.39:1). Use the pixel dimensions when precision matters.

What is the difference between letterboxing and pillarboxing?

Letterboxing adds bars above and below the picture, usually when wide content is shown on a narrower screen. Pillarboxing adds bars at the sides, usually when narrow content is shown on a wider screen.