HTML Guide for width
The width and height attributes on <img> elements expect a digit to specify the dimension in pixels. It should not contain units, letters or percent signs.
You can achieve this using CSS instead, for example:
<!-- Invalid syntax, the height attribute expects only digits -->
<img src="photo.jpg" alt="cat" height="auto" />
<!-- Valid syntax using CSS -->
<img src="photo.jpg" alt="cat" style="height: auto" />The width attribute on the img element must be a positive integer representing the number of pixels.
The HTML img element’s width and height attributes are expected to specify image dimensions in pixels. According to the HTML Living Standard, these attributes accept only non-negative integers. These integers define the rendered dimension of the image, overriding the actual image size based on its native resolution. The value “auto” is not a valid integer, which leads to the validation error you’ve encountered.
Here is a correct usage example of the img element:
<!DOCTYPE html>
<html lang="en">
<head>
<title>Valid Image Width</title>
</head>
<body>
<img src="example.jpg" alt="Example image" width="200" height="100">
</body>
</html>In the example above, the width is set to 200, and the height is set to 100. Both values are non-negative integers representing pixel dimensions. If you intend to maintain the image’s aspect ratio while adjusting another dimension, you can omit one of the attributes, and modern browsers will automatically adjust the aspect ratio based on the given dimension.
The error message is indicating that the width attribute of the <video> element has an invalid value. According to the HTML specification, the width attribute expects a non-negative integer value, representing the pixel width of the video.
The value "auto" is not valid for the width attribute. Instead, specify a full number that indicates the pixel width of the video. If you want the video to be responsive without specifying a fixed width, you can use CSS to achieve that.
Here are two ways to resolve this:
-
Specify a valid pixel value for width:
<video width="640" height="360" controls> <source src="video.mp4" type="video/mp4"> Your browser does not support the video tag. </video> -
Use CSS for a responsive video player:
Instead of using the width attribute, use CSS to set the width of the video element. This allows the video to adjust its size according to the container or viewport.
<style> .responsive-video { width: 100%; height: auto; } </style> <video class="responsive-video" controls> <source src="video.mp4" type="video/mp4"> Your browser does not support the video tag. </video>
In the second example, the video will scale based on its containing element, maintaining its aspect ratio due to the height: auto; CSS rule. This approach offers more flexibility for responsive design.
The sizes attribute is used to complement the srcset attribute on an <img> tag for responsive images. When this attribute is present, all image candidates must specify its width.
The attributes width and height of <iframe> elements expect a non-negative integer, so an empty string is not allowed. Either define the correct dimension, or remove this attribute.
The attributes width and height of <img> elements expect a non-negative integer, so an empty string is not allowed. Either define the correct dimension, or remove this attribute.
The srcset attribute requires a width descriptor (w) or pixel density descriptor (x) for each image candidate when the sizes attribute is present.
When using the sizes attribute on an img element, each entry in srcset must include either a width descriptor (e.g., 860w) or a pixel density descriptor (e.g., 2x). This tells browsers how to select the most appropriate image source for the current viewport or display density. Omitting the descriptor leads to HTML validation errors and unexpected image selection.
Correct usage with width descriptors:
<img
alt=""
sizes="(min-width:568px) 140px"
srcset="photo.png?w=860&q=90 860w"
src="photo.png?w=860&q=90">Correct usage with pixel density descriptors (if sizes is removed):
<img
alt=""
srcset="photo.png?w=860&q=90 2x"
src="photo.png?w=860&q=90">Key points:
- With sizes, use width descriptors (e.g., 860w).
- Without sizes, you may use pixel density descriptors (e.g., 2x).
- Always use either px or w units in the sizes attribute values; do not use w.
The sizes attribute is used to complement the srcset attribute on an <img> tag for responsive images. When this attribute is present, all image candidates must specify its width.
The attributes width and height on an iframe expect a valid positive integer without any decimals.
Here’s an example of incorrect code where decimals are being used for dimension attributes:
<iframe src="example.html" height="602.88" width="800.2"></iframe>Corrected code without decimals:
<iframe src="example.html" height="603" width="800"></iframe>In the corrected code, the width and height values has been changed to a whole number, which conforms to the standard integer value expected by the W3C validator.
The attributes width and height on an iframe expect a valid positive integer without any decimals.
Here’s an example of incorrect code where decimals are being used for dimension attributes:
<img src="photo.jpg" alt="Dog" height="602.88" width="800.2">Corrected code without decimals:
<img src="photo.jpg" alt="Dog" height="603" width="800">In the corrected code, the width and height values has been changed to a whole number, which conforms to the standard integer value expected by the W3C validator.
The <iframe> element, used to embed another document inside the current document, accepts both attributes width and height which must be valid non-negative integers. Percentages are not allowed for these attributes.
<img> elements accept a width attribute to specify the size in pixels. This value can only be an integer, it should not contain units or %. If you need to specify a percentage width, you can do that with CSS:
<img src="photo.jpg" alt="red car" style="width:100%;"><video> elements accept a width attribute to specify the width in CSS pixels. This value can only be an integer, it should not contain units or %. If you need to specify a percentage width, you can do that with CSS.
Here’s an example of setting width and height on a video element.
<video controls width="640" height="480">
<source src="/media/cc0-videos/flower.webm" type="video/webm">
</video>Attribute values for width and height on the object element must be a valid integer (pixels), not a percentage.
In HTML5, the width and height attributes for the <object> element must be specified in pixels as an integer value, such as height="500". Using percentage values like height="100%" is not allowed in the attribute according to the HTML living standard and will trigger a validation error. To set a percentage height, use the CSS width and height properties instead.
Correct usage (pixels via attribute):
<object data="example.pdf" type="application/pdf" width="600" height="400"></object>Correct usage (percentage via CSS):
<object data="example.pdf" type="application/pdf" style="width: 100%; height: 100%;"></object>Example of a full valid HTML document using CSS for 100% height:
<!DOCTYPE html>
<html lang="en">
<head>
<title>Object Height Example</title>
<style>
html, body {
height: 100%;
margin: 0;
}
object {
height: 100%;
width: 100%;
display: block;
}
</style>
</head>
<body>
<object data="example.pdf" type="application/pdf"></object>
</body>
</html>The width and height attributes on <img> and <iframe> elements expect a digit to indicate the number of pixels. Ensure that this attribute contains only digits.
For example:
<!-- This is invalid because width is not a digit -->
<img width="225px" height="100px" alt="cat" src="cat.jpg" />
<!-- This is valid -->
<img width="225" height="100" alt="cat" src="cat.jpg" />The value px for a width property is incorrect, it should include both the value and the units, like 10px, or just 0 if it’s zero width. Using only the units without the value is incorrect.
Example of Incorrect CSS
<style>
.example {
width: 300; /* This is missing the unit */
}
.example2 {
width: px; /* This is missing the value */
}
</style>Corrected Example of CSS
Make sure to include the unit (like px, em, %, etc.) when specifying the width:
<style>
.example {
width: 300px; /* Correctly includes 'px' unit */
}
</style>Conclusion
Always ensure to provide proper units when specifying dimensions in CSS. Common units are:
- px (pixels)
- em (relative to the font size of the element)
- % (percentage of the parent element’s width)
Using the width attribute with an invalid value or on an element where it’s not allowed causes a “types are incompatible” error.
The width attribute must only be used on certain elements, like img, canvas, input (of type image), or video. Its value should be a valid integer, representing the number of CSS pixels, without units. Using CSS units like px or % directly in the attribute, or placing the attribute on unsupported elements, will trigger this validation message.
Correct usage:
<img src="photo.jpg" width="400" alt="Sample photo">Incorrect usage (with units):
<img src="photo.jpg" width="400px" alt="Sample photo">Incorrect usage (on unsupported element):
<div width="400">Content</div>To set width via CSS instead, use the style attribute or an external stylesheet:
<div style="width: 400px;">Content</div>For styling, always use CSS when possible; reserve the width attribute for the few HTML elements that specifically support it, and ensure the value is a simple number without units.
The value specified for a width attribute in CSS is not valid.
The width CSS property sets an element’s width. There are many allowed values for this attribute, for example:
/* <length> values */
width: 300px;
width: 25em;
/* <percentage> value */
width: 75%;
/* Keyword values */
width: max-content;
width: min-content;
width: fit-content(20em);
width: auto;
/* Global values */
width: inherit;
width: initial;
width: revert;
width: unset;Both <table> and <td> elements no longer accept a width attribute. Instead, you should use CSS as in this example:
<table style="width:100%;">
<tr>
<td style="width:50px;">Name</td>
</tr>
</table>