HTML Guide
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" />Related W3C validator issues
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 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 W3C HTML Validator issue you encountered indicates that the value of the height attribute for an <img> element is set to “100%”, which is not allowed in HTML. The height attribute must be a specific digit that represents the height in pixels (e.g., “150”), rather than a percentage or any other unit.
How to Fix the Issue
To resolve this issue, you need to specify a numeric value for the height attribute instead. If you want the image to occupy a certain percentage of the container, use CSS instead of the height attribute.
Example of Incorrect HTML
Here is an example that causes the validation issue:
<img src="image.jpg" height="100%" alt="Example Image">Corrected HTML Using Pixel Values
To correct the issue, replace the percentage with a pixel value:
<img src="image.jpg" height="200" alt="Example Image">Alternative: Using CSS for Responsive Design
If you want the image to scale responsively and occupy 100% of the width of its container, consider using CSS:
<style>
.responsive-img {
width: 100%;
height: auto; /* Maintains aspect ratio */
}
</style>
<img src="image.jpg" class="responsive-img" alt="Example Image">Summary
- Do not use percentage values for the height attribute of <img> tags.
- Use pixel values for fixed dimensions.
- For responsive design, use CSS to set the dimensions instead.
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 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 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 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.
<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%;">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>