How do you find the width and height of an image in html?

Example

An image with a height of 600 pixels and a width of 500 pixels:

Try it Yourself »

The width attribute specifies the width of an image, in pixels.

Tip: Always specify both the height and width attributes for images. If height and width are set, the space required for the image is reserved when the page is loaded. However, without these attributes, the browser does not know the size of the image, and cannot reserve the appropriate space to it. The effect will be that the page layout will change during loading (while the images load).

Tip: Downsizing a large image with the height and width attributes forces a user to download the large image (even if it looks small on the page). To avoid this, rescale the image with a program before using it on a page.

Browser Support

Syntax

Attribute Values

❮ HTML

Example" width="200" height="100">

Example

Sample image
(width:193px, height:130px)

Example" width="193" height="130"> (width:193px, height:130px)


Example" width="96" height="65"> (width:96px, height:65px)


Example" width="100%" height="130"> (width:100%, height:130px)

Output

(width:193px, height:130px)

(width:96px, height:65px)

(width:100%, height:130px)

• 18 min read
• Browsers, Performance, Optimization, Core Web Vitals

Web performance advocates have often advised to add dimensions to your images for best performance to allow the page to be laid out with the appropriate space for the image, before the image itself has been downloaded. This avoids a layout shift as the image is downloaded — something Chrome has recently started measuring in the new Cumulative Layout Shift metric.

Well, a dirty, little, secret — not that well-known outside the hard-core web performance advocates — is that, until recently, this actually didn’t make a difference in a lot of cases, as we’ll see below. However, adding width and height attributes to your

This might render in two stages, first as the HTML is downloaded, and then second once the image is downloaded. With the above code, this would cause the main content to jump down after the image is downloaded and the space needed to display it can be calculated:

Layout shifts are very disrupting to the user, especially if you have already started reading the article and suddenly you are thrown off by a jolt of movement, and you have to find your place again. This also puts extra work on the browser to recalculate the page layout as each image arrives across the internet. On a complex page with a lot of images this can place a considerable load on the device at a time when it’s probably got a lot of better things to deal with!

The traditional way to avoid this was to provide width and height attributes in the

Then the render happens like below, where the appropriate amount of space is set aside for the image when it arrives, and there is no jarring shift of the text as the image is downloaded:

Even ignoring the annoying impact to the user in content jumping around (which you shouldn’t!), the impact on the CPU can also be quite substantial. The below screenshot shows the performance calculations performed by Chrome on a site I work on which has a gallery of about 100 images. The left-hand side shows the calculations when width and height are provided, and on the right when they are not.

As you can see, the impact is considerable — especially on lower-end devices and slow network speed, where images are coming in separately. This increases load time by a noticeable amount.

How CSS Interacts With Element Widths And Heights

Widths and heights on an image can cause issues when you try to alter them using CSS. For example, if you want to limit your images to a certain width you might use the following CSS:

img {
  max-width: 100%;
}

This will override the width of the image and constrain it when necessary, but if you have explicitly set the height on the image tag, then we are not overriding that (only the width) and you will end up with a stretched or squashed image, as we have no longer maintained the aspect ratio of the image:

This is actually very easily fixed by adding a height: auto line to the CSS so the height attribute from the HTML is overridden too:

img {
  max-width: 100%;
  height: auto;
}

However, I find it still catches people by surprise and sometimes leads to them not specifying image dimensions in the HTML instead. With no image dimensions, you can get away with just specifying max-width: 200px in the CSS without having to specify height: auto and the browser will automatically figure out the height itself — once it has the image.

So, once we add the dimensions and that the height: auto trick, we get the best of both worlds, right? No layout shifts, but also the ability to resize images using CSS? Well until very recently you might have been surprised to find out the answer was in fact: no (I was — hence why I decided to write this article).

For example, take the code below:

Your title
Introductory paragraph.

Lorem ipsum dolor sit amet, consectetur…

This would have resulted in this load:

Wait, what’s going on here? We’re back to the first problem. I thought I said that by specifying the image dimensions in the HTML you could avoid this layout shift problem? Well, this is where it gets interesting and will lead on to the main point of this article.

The problem is that, unless you were giving explicit width and height CSS values to your images — and who wants to limit themselves like that in a responsive world where you want the image to expand or shrink to fill up the available space — then CSS will need the dimensions from the image file itself to figure out the auto part of the dimensions. It ignored any width and height attributes set in the HTML.

The implication of all this is that specifying width and height attributes on images often wasn’t actually that useful in a lot of cases. Yes, when an image is being shown at full size, without any CSS changing any dimensions, it is useful to resolve the layout shifting problem. However, when you use CSS like below to ensure images do not overflow their available space, then you run into problems as soon as the available width becomes smaller than the actual image size.

img {
  max-width: 100%;
  height: auto;
}

This affects any page where we constrain the image size in a responsive manner — i.e. small screen mobile devices. These are likely to be the very users suffering with network constraints and limited processing power that will suffer most from layout shifts! Of course, we ideally should be delivering appropriately sized images for the screen size, but you cannot cover every device size, so often images will need some resizing by the browser, particularly on mobile.

Many websites may not bother to specify widths and heights on their

Rather than hard-coding the aspect-ratio, this uses the attr CSS function to create the appropriate aspect-ratio based on the image width and height attributes provided by the HTML. The attr function has been around for a while, but has been very limited in scope — it’s supported for content by all browsers, but not for the wider use case of any other attribute like width and height, which is what is needed here.

If attr was able to be used for the well-known width and height attributes from img elements, then it could use be used to automatically calculate the aspect-ratio as per above. This would solve issue 1 (no hard-coded aspect ratio needs to be set in the HTML nor the CSS), issue 2 (very simple to add) and, as we shall see, there is a very simple answer to issue 3 (adoption).

Basically, this solution means if the following four conditions are true, then the correct image dimensions could be calculated without needing to wait for the images to download, and so without the need of a content layout shift:

• height is set on the element in HTML
• width is set on the element in HTML
• height (or width) is set in the CSS — including using percentage values like max-width: 100%;
• width (or height) is set to auto in the CSS.

If any one of these were not set, then the calculation would not be possible, and so would fail and be ignored and have to wait for the image to be downloaded.

So once browsers support using the HTML width and height to calculate the aspect-ratio we can solve our problem very simply with no change in practice to HTML and one line of CSS code! As mentioned above, this is also something many web developers may have already assumed was happening anyway.

Driving Adoption Of This Solution

Because this is just a CSS attribute, the proposal contained a further twist — it could be added to the user-agent stylesheet used by browsers so would not even require any changes from web developers to benefit from this.

The user-agent stylesheet is where default CSS definitions are set (e.g. what font-size the h2 element uses), which can be overridden by your own CSS if you want. By adding the above aspect-ratio one-liner to this we don’t need to drive adoption — we basically turn it on automatically for all sites that meet the above four conditions!

However, this does depend on the attr function having access to the width and height HTML attributes, and also the upcoming aspect-ratio CSS property to be completed — neither of which has happened yet. So instead, as an easier fix, the browsers could implement the equivalent logic deep in rendering code rather than exposing it via the user-agent stylesheet, but the effect is the same. This alternative implementation approach was even suggested as part of the proposal.

Firefox went ahead and did this as an experiment and then turned it on by default for Firefox 71. Once that was released, then your site may well have just got faster for free — thanks Mozilla! Maybe in future, they will move this to the user-agent stylesheet method, but for now, this is sufficient (and perhaps more performant?).

Backwards Compatibility

When introducing a change in behavior, there is always a concern about backwards compatibility and this feature was no different. In theory, as long as the four attributes were appropriately set, there should be no breakage with this.

However, when Firefox initially experimented with it, they discovered problems for those setting the width and height incorrectly in their HTML. Whereas previously these incorrect values would be ignored if the CSS overrode them, now they were being used when auto was set and the images were not displayed correctly and led to squished or stretched images. Now you could argue that web developers shouldn’t set these values incorrectly, and in some cases, it would be already broken even without this change (the case above when you didn’t set height: auto), but still, breaking sites is never a good thing. That is also something the web tries very hard to avoid — and is mostly very good at avoiding that (it’s one of my favorite things about the web as a platform).

The solution to that problem, however, was relatively simple: have the actual image aspect-ratio of the image override any CSS calculated aspect-ratio. This way the (incorrectly) calculated aspect-ratio can be used for initial layout, but then can be recalculated when the image is downloaded, so the image is displayed as it was before. This does cause a layout shift (since the incorrect space was allocated initially) but that was happening before anyway, so it’s no worse. In fact, it’s often a lot better as an incorrect aspect ratio will often be closer to the truth than a zero aspect-ratio.

Rollout To Other Browsers

After Firefox’s successful experimentation, Chrome also decided to implement this (again using the layout coded method for now rather than default user-agent stylesheet), and rolled it out by default in Chrome 79. This also took care of the other chromium-based browsers (Edge, Opera and Brave, for example). More recently, in January 2020, Apple added it to their Tech Preview edition of Safari, meaning it should hopefully be coming to the production version of Safari soon, and with that, the last of the major browsers will have implemented this and the web will become better and less jolty for a huge number of sites.

Limitations

There are a few limitations to be aware of with this feature, including issues with:

• Art Direction
• Lazy Loading
• Non-Images

Art Direction

The fix works great to calculate the aspect-ratio based on a fixed width and height, but what about when those change? This is known as art direction and an example is shown below:

In this case we are using a wide image for desktop, and then a square, cropped image for mobile. Responsive images can be implemented with the picture element like this:

Currently, this only allows the width and height to be set once on the main, fallback

Perfect! Well, unfortunately, I discovered this height and width solution is not compatible with the recently released native lazy-loading functionality as can be seen on this test page. I’ve raised a bug for this issue and hopefully the Chrome team will fix this soon. (Update: This was fixed in Chrome 83.)

Non-Images

Currently, the browsers that have implemented this, have only done for the

(jw, yk, il)

How do you write the width and height of an image in HTML?

The height and width of an image can be set using height and width attribute. The height and width can be set in terms of pixels. The height attribute is used to set the height of the image in pixels. The width attribute is used to set the width of the image in pixels.

How do you check the size of an image in HTML?

The width attribute specifies the width of an image, in pixels. Tip: Always specify both the height and width attributes for images. If height and width are set, the space required for the image is reserved when the page is loaded.

How do you find the width and height in HTML?

CSS height and width Examples.

Set the height and width of a

element: div { height: 200px; width: 50%; ... .

Set the height and width of another

element: div { height: 100px; width: 500px; ... .

This

element has a height of 100 pixels and a max-width of 500 pixels: div { max-width: 500px; height: 100px;.

How do I manage the size of an image in HTML?

Step 1: Firstly, we have to type the Html code in any text editor or open the existing Html file in the text editor in which we want to change the size of an image. Step 2: Now, place the cursor inside the img tag. And then, we have to use the height and width attribute of the img tag for changing the size of an image.

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