What is the most common aspect ratio?

16:9 dominates televisions, monitors, laptops and online video, and was fixed as the high definition standard by ITU-R Recommendation BT.709. Photography still leans on 3:2 from 35mm film and 4:3 from many phone sensors, and vertical 9:16 has become the default for short-form social video.

How do I resize an image without distorting it?

Change one dimension and let the other follow the ratio. Enter the original width and height here, type the width you want, and use the calculated height. Multiplying both dimensions by the same factor works equally well; typing each by hand does not.

What causes black bars on a video?

A mismatch between the shape of the picture and the shape of the screen. Content wider than the display is letterboxed with bars above and below, and content narrower is pillarboxed with bars at the sides. The bars preserve the whole image instead of cropping it away.

Is 21:9 really 21 by 9?

Not exactly. A 2560 by 1080 panel reduces to 64:27, a decimal ratio of 2.37, and a 3440 by 1440 panel reduces to 43:18, or 2.39. Neither is 21:9, which would be 2.33. The label is a marketing rounding that keeps the nine so it compares easily against 16:9.

Why does my ratio reduce to odd numbers?

Because the greatest common divisor of your width and height is small. A 1366 by 768 panel reduces to 683:384, which no standard matches, which is why that resolution is a slightly awkward near-16:9 shape. The closest standard row tells you how far off it sits.

Does aspect ratio affect image quality?

Not by itself, but changing it does. Scaling both dimensions by the same factor preserves the picture, while stretching one dimension distorts every shape in the frame and cropping discards content permanently. Total pixels, not ratio, is what determines detail and file size.

Aspect Ratio Calculator

Works anywhere

Reduces a width and height to their simplest whole-number ratio, names the closest broadcast or cinema standard, scales the image to any target width without distorting it, and shows the bar size when the shape is shown on a 16:9 screen. 1920 by 1080 reduces to 16:9.

Results

Worked example. Edit the values and press Calculate

Aspect ratio

16:9

Decimal ratio
1.7778
Width divided by height. Multiply a width by this to get the matching height's reciprocal.
Closest standard ratio
16:9
An exact match for this standard.
Height at your target width
720 px
Scaling to 1,280 px wide keeps the shape identical.
On a 16:9 screen
Fills the frame, no bars
Orientation
Landscape
Total pixels
2,073,600
Megapixels
2.07
Diagonal (pixels)
2,202.9

Why use this calculator

Aspect ratio is the one property of an image that cannot be changed without damage. Resize proportionally and nothing is lost; change the ratio and either the picture is stretched, which viewers notice instantly on faces, or content is cropped away, which is worse when the cropped part is the subject.

This calculator does the three jobs that come up constantly: reduce a resolution to the ratio people actually quote, work out the exact height for a new width so a resize stays faithful, and predict how much of the screen will be black bars when a shape is played back on a standard 16:9 display.

It also names the closest recognised standard, which is how you discover that a file is very slightly off spec.

How to use it

Enter the width and height in pixels exactly as your file, camera or display reports them; the file properties panel or the video editor's clip information shows both.
Enter the width you want to scale to in the resize field, and the calculator returns the height that preserves the shape, rounded to the nearest whole pixel.
If you are checking a display rather than a file, use its native resolution rather than the resolution currently set, because running a panel off its native resolution is itself a source of softness.
Read the closest standard row to confirm the file is on spec, and the 16:9 row to see what a normal screen will do with it.

What each result means

Aspect ratio: The width and height reduced to their smallest whole numbers, which is the form people quote, such as 16:9.
Decimal ratio: Width divided by height as a single number. It is the value to compare when two ratios look similar, such as 1.85 and 16:9.
Closest standard ratio: The nearest recognised broadcast, photographic or cinema format, with how far the resolution sits from it.
Height at your target width: The height that keeps the shape unchanged at your new width, rounded to a whole pixel.
On a 16:9 screen: Whether this shape letterboxes, pillarboxes or fills a standard widescreen display, and how deep the bars would be.
Orientation: Whether the frame is wider than it is tall, taller than it is wide, or exactly square.
Total pixels: Width times height, which drives file size, encoding time and the rendering load on a device.
Megapixels: The same pixel count in millions, the unit cameras and phone specifications use.
Diagonal (pixels): The corner-to-corner pixel distance, needed to convert a diagonal screen size in inches into pixel density.

The formula

The simplified ratio is width divided by the greatest common divisor of width and height, expressed against height divided by that same divisor. The decimal ratio is simply width divided by height.

A proportional resize uses new height = target width times original height divided by original width

On a display of ratio S, a content ratio R wider than S is letterboxed with bars occupying (1 minus S divided by R) divided by two of the screen height at the top and the same at the bottom, and a narrower ratio is pillarboxed by the mirror-image formula across the width.

How this number is used in practice

Letterboxing is the visible consequence of a mismatch, and it is not a defect. Cinema shoots wider than television broadcasts: the common flat format is 1.85:1 and scope is 2.39:1, while a television is 16:9, which is 1.778:1. Playing a scope film on a 16:9 television leaves bars covering just under thirteen per cent of the screen height at the top and the same at the bottom.

The alternative, cropping the sides to fill the screen, throws away a quarter of the image and was the reason pan-and-scan releases were so disliked.

Social and video platforms turned the same problem into a daily one. A vertical 9:16 clip shown on a widescreen player is pillarboxed with very deep bars, while a 16:9 video on a phone held upright fills only a strip in the middle. Producing a master at one ratio and then deliberately reframing for the others, rather than letting a platform crop automatically, is the difference between a subject centred in frame and a subject with their head cut off.

For still images and web layout the practical rule is to fix one dimension and derive the other. Set the width a layout requires, take the height from this calculator, and the image is never stretched. Where a fixed box must be filled at a different ratio, crop deliberately to the box rather than scaling non-uniformly, because a two or three per cent stretch is invisible on a landscape and obvious on a face.

Worked examples

A 1920 by 1080 full HD frame resized to 1280 wide
Reduces to 16:9, a decimal ratio of 1.7778, and scales to 720 pixels high with 2,073,600 total pixels.
A 2560 by 1600 laptop panel
Reduces to 8:5, which is the 16:10 standard, and holds 4,096,000 pixels or 4.10 megapixels.
A 2.39:1 cinema frame at 2048 by 858
Letterboxed on a 16:9 television with bars covering 12.8% of the screen height at the top and the same at the bottom.
A vertical 1080 by 1920 social clip
Reduces to 9:16, is flagged as portrait, and pillarboxes a 16:9 player with bars across 34.2% of the width on each side.

When people use it

Resizing an image or video for the web without stretching it
Checking that an exported file matches the ratio a platform expects
Choosing between a 16:9 and an ultrawide monitor for a desk
Working out how much of a screen black bars will occupy before a screening
Setting the correct canvas size for a thumbnail, banner or social post

Tips

Always fix one dimension and calculate the other. Typing both by hand is how images end up subtly stretched.
16:9 is 1.778:1, so a 1.85:1 flat cinema frame still letterboxes on a television, just very slightly.
21:9 monitors are usually 2560 by 1080, which is 64:27, or 3440 by 1440, which is 43:18. Neither is exactly 21:9; the marketing name is rounded.
Non-square pixels exist in older broadcast formats, so a 720 by 576 file can legitimately display as 16:9 despite its pixel count.
When a fixed box must be filled at a different ratio, crop deliberately rather than scaling non-uniformly. A stretch is far more visible than a crop.
Shoot or export a wider master than your narrowest delivery ratio, so there is room to reframe rather than crop into the subject.

What it assumes, and where it stops being accurate

Pixels are square, which is true of every modern display, camera and web image but not of some legacy broadcast formats.
Width and height are whole pixels; fractional inputs are floored before the ratio is reduced.
The framing row compares against a 16:9 display, because that is the dominant television and monitor shape.
The closest standard is chosen by smallest decimal difference and may be slightly off if a resolution sits between two formats.
Resize heights are rounded to the nearest whole pixel, so very large scale factors can differ from the exact ratio by a fraction of a pixel.

Terms used on this page

Aspect ratio: The proportional relationship between an image's width and its height, written as two numbers separated by a colon.
Letterbox: Black bars added above and below a picture that is wider than the display it is shown on.
Pillarbox: Black bars added to the left and right of a picture that is narrower than the display.
Greatest common divisor: The largest whole number that divides both dimensions exactly, used to reduce a ratio to its simplest form.
Scope: The 2.39:1 anamorphic widescreen cinema format, the widest ratio in common theatrical use.

Questions people ask

What is the most common aspect ratio?: 16:9 dominates televisions, monitors, laptops and online video, and was fixed as the high definition standard by ITU-R Recommendation BT.709. Photography still leans on 3:2 from 35mm film and 4:3 from many phone sensors, and vertical 9:16 has become the default for short-form social video.
How do I resize an image without distorting it?: Change one dimension and let the other follow the ratio. Enter the original width and height here, type the width you want, and use the calculated height. Multiplying both dimensions by the same factor works equally well; typing each by hand does not.
What causes black bars on a video?: A mismatch between the shape of the picture and the shape of the screen. Content wider than the display is letterboxed with bars above and below, and content narrower is pillarboxed with bars at the sides. The bars preserve the whole image instead of cropping it away.
Is 21:9 really 21 by 9?: Not exactly. A 2560 by 1080 panel reduces to 64:27, a decimal ratio of 2.37, and a 3440 by 1440 panel reduces to 43:18, or 2.39. Neither is 21:9, which would be 2.33. The label is a marketing rounding that keeps the nine so it compares easily against 16:9.
Why does my ratio reduce to odd numbers?: Because the greatest common divisor of your width and height is small. A 1366 by 768 panel reduces to 683:384, which no standard matches, which is why that resolution is a slightly awkward near-16:9 shape. The closest standard row tells you how far off it sits.
Does aspect ratio affect image quality?: Not by itself, but changing it does. Scaling both dimensions by the same factor preserves the picture, while stretching one dimension distorts every shape in the frame and cropping discards content permanently. Total pixels, not ratio, is what determines detail and file size.

Use this with

Aspect Ratio Calculator answers one part of the question. These pick up where it stops: Screen PPI Calculator, Data Storage Converter, Area Calculator and Ratio Calculator.

Where these figures come from

Works anywhereLast reviewed 2026-09·How we build and check calculators

This calculation is jurisdiction-neutral arithmetic. No country-specific rules are applied.

ITU-R: Recommendation BT.709. The recommendation that fixed 16:9 as the HDTV picture aspect ratio
SMPTE: Society of Motion Picture and Television Engineers. Standards body for cinema and broadcast image formats
VESA: Video Electronics Standards Association. Display resolution, timing and DisplayHDR standards

Aspect Ratio Calculator produces an estimate for general information. It is not financial, tax, medical, legal or engineering advice. read the full disclaimer. Spotted a wrong number? Report it and it gets fixed. The form picks up this calculator and the inputs you used.