Calculate Ratio Image

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  1. Image Size Ratio Calculator
  2. Calculate Ratio Images
  3. Calculate Ratio Of 2 Numbers
  4. How To Calculate Image Ratio

So punch that into the aspect ratio calculator above and you get: padding-bottom: 3333333%; I then set: the background-color for the border when the image is the wrong dimensions. The background-size to contain so that the image will scale down horizontally and vertically. Originally you have an image of size (wxh) 500x1000, this width/height ratio is 0.5. Assuming you are changing 1000 to 768 in height, your result width would be 0.5. 768 = 384. Another example, 1800 x 1200 and your new height is 200, then your new width is 300 because 300/200 is 1.5 and 1800/1200 is also 1.5. Calculate new Width (w1). Aspect ratio = 400/300 = 1.3333 Therefore new width = 200 / 1.3333 = 150. Another way of looking at it is, aspect ratio =4:3. So (200/4).3 = 150. 16:9 Aspect Ratio. Aspect Ratio of 16:9 ('Sixteen-by-Nine' and 'Sixteen-to-Nine') which is also known as High Definition (HD) became leading aspect ratio since the start of the 21st century. It is the international standard format of HDTV, non-HD digital television and analog widescreen television PALplus.

So I’ve had to do a lot of stuff using aspect ratios lately, and I got tired of constantly having to do the math, so I’ve put together a CSS aspect ratio calculator (below) that should help save you a bit of time and energy.

Aspect Ratio Calculator

Simply put in the dimentions of your element and let the Aspect Ratio Calculator figure out the padding-bottom.

padding-bottom: 100%

Aspect Ratios Explained

The “aspect ratio” is the correlation between the height and width of an element.

Think of the way an image scales down its height in proportion to its width in responsive design.

Now, with images it’s easy to achieve, but when it comes to iframes, embeds and <div>’s it can be a little tricky.

Padding-bottom to the rescue

So the best way to make elements use an aspect ratio is to set the height to 0 and give the padding bottom as a percentage.

This is because when you set the padding-bottom as a percentage, it will be worked out as a percentage of the width.

So for example.

You have an empty <div> and it’s container has a width of 200px.

You set the padding-bottom to be 50%.

So it’s actual height will be 100px.

Because 50% of 200 is 100.

And what’s so powerful about this, is that when that then scales down to 146px, it’s height will be 73px (which is still in proportion to its width).


Making this super awesome for responsive web design.

So how do you work out the padding-bottom?

Well you can always use the calculator above – that’s why I made it. I’m always forgetting how to do the equation and it takes energy…but here’s how it works, if you want to do it manually:


“h” represents the height of your element and “w” represents the width.

So basically divide the width of your element by 100 and then divide the height of your element by that.

Easy enough but it takes some thinking about.

Wrapping it all up with some examples

So now you understand the core concept, here’s some examples of how to use it with the full CSS.

Image Size Ratio Calculator

Example 1: Videos – YouTube, Vimeo etc. (most common)

This is the most common use of this method and you might not need to even work out the aspect ratio as there are some pretty common sizes (shown in the code below).

You basically create a wrapping <div> that does all the aspect ratio stuff.

Calculate Ratio Images

Then place your video inside it with absolute positioning.

Example 2: Image slider (with varying image sizes)

This ones a little more complicated but is very, very useful.

I actually come up with this the other day when I was trying to build a slider for a small electronics store.

The situation was as follows:

  • They’re a small company that need to be able to manage the site themselves.
  • On a monthly basis, companies send them banners promoting offers on their products (i.e Panasonic might send them through a banner that advertises a 2 year warranty).
  • They’re dealing with upwards of 30 companies – none of whom send through banners the same size.

So the problems are:

  • Each banner needs to be sliced to fit the slider (as there is information all over the banners that cannot be cropped off).
  • They have nobody in-house that has Photoshop skills (or Photoshop for that matter).
  • They are a small company and want their monthly budget to go into work that will make them money (i.e SEO and social media marketing)

I needed to build an image slider that you could upload any sized image in without it looking crap or making the page jump all over the place as the slider does it’s thing.

So my initial thought was to use an image with a max width and height, inside a <div> with a set height, styled as a table cell, with the vertical-align set to middle.

The wrapping <div> would then have a background-color that would work as a border for images that don’t fit the right proportions of the slider.

That worked fine until it went on to mobile.

Because the height needed to respond to the width of the element.

So my next attempt was to try using the aspect ratio with a background-image.

Which worked perfectly and only took me about an hour to implement.

My slider is 750px wide by 274px tall.

So punch that into the aspect ratio calculator above and you get:

padding-bottom: 36.53333333333333%;

Calculate Ratio Image

I then set:

  • the background-color for the border when the image is the wrong dimensions.
  • the background-size to contain so that the image will scale down horizontally and vertically.
  • the background-position to 50% 50% so it will be centered horizontally and vertically.
  • the background-repeat to no-repeat so it didn’t repeat the image in the spaces I want the background-color to fill.

After that it was just a case of outputting the image as a background-image on the specific slide.

Here’s my full code:

You’ll notice I also put the <img> inside the anchor tag with a class of hidden – this is because the browser wont download an elements background-image if it is not visible on the page.

Creating a flashing effect as the slide changes, whilst the browser downloads the image.

So a work around is to load in the actual image inside an <img> tag and hide it using CSS – as the browser will download images inside an <img> tag whether or not they are visible.

Final words

There’s a lot more examples of how you can use this aspect ratio method in web design, but this post wasn’t really about that. It was just to share this new tool and hopefully give an insight into how you can utilize the aspect ratio concept in your projects.

If you like this tool or found this useful feel free to bookmark the page and remember to share this on social media.

Last thing, I want to know how you use aspect ratio in your projects?

Have you made something different that you can share with us all in the comments?

Let me know.


Use this ratio calculator to check the dimensions when resizing images ✅.

You might not be aware of this fact, but every frame, digital video, canvas, responsive design, and image often has a rectangular shape that is exceptionally precise in proportion (or ratio).

The ratio has to be well-defined to make shapes fit into different and distinct mediums, such as computer, movies, television and camera screens.

Image Aspect Ratio

To fit ratios in a variety of mediums is often a challenge to designers, particularly if they have to crop and convert content.

Luckily, having an aspect ratio calculator makes things easier. If you are working on a digital video, it is essential to initially compress the files of the digital video in order to get the accurate dimensions (or aspect ratios) of the video.

This requires a lot of calculations. And that’s where an aspect ratio calculator comes in to help make these calculations accurate. To get exact formats for your video, just enter one dimension and the calculator will compute the other dimension.

What is Aspect Ratio?

You have to understand what aspect ratios are in order to easily move designs, images and compress digital video files/content from one medium to another without making any error in your calculations. For the record, the proportional relationship between the height and width of a rectangle is what is aptly referred to as an aspect ratio.

Aspect ratio calculations matter a lot depending on whether it is an image, design project or a digital video you are working with.

Calculate Ratio Image

Aspect ratios are largely defined by numbers, as in a mathematical ratio that clearly defines how many inches high and how many inches wide your video, image and design projects should be. While aspect ratios are measurements of the height and width, they are often reduced to the smallest usable ratio in order to fit perfectly in every medium.

To achieve a perfect aspect ratio, you must employ the use of an aspect ratio calculator. It reduces any margin of error. Check the what is aspect ratio post.

Visit for all of your projector and projector screen needs for all aspect ratios.

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How To Calculate Image Ratio

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