# Bad value for attribute “srcset” on element “source”: No width specified for image X. (When the “sizes” attribute is present, all image candidate strings must specify a width.)
> Canonical HTML version: https://rocketvalidator.com/html-validation/bad-value-for-attribute-srcset-on-element-source-no-width-specified-for-image-x-when-the-sizes-attribute-is-present-all-image-candidate-strings-must-specify-a-width
> Attribution: Rocket Validator (https://rocketvalidator.com)
> License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/)
The `srcset` attribute supports two types of descriptors: **width descriptors** (like `480w`) and **pixel density descriptors** (like `2x`). However, these two types cannot be mixed, and the `sizes` attribute is only compatible with width descriptors. The `sizes` attribute tells the browser how wide the image will be displayed at various viewport sizes, and the browser uses this information along with the width descriptors in `srcset` to choose the most appropriate image file. If `sizes` is present but an image candidate lacks a width descriptor, the browser cannot perform this calculation correctly.
This matters for several reasons. First, it violates the [WHATWG HTML specification](https://html.spec.whatwg.org/multipage/images.html#srcset-attributes), which explicitly requires that when `sizes` is present, all image candidates must use width descriptors. Second, browsers may ignore malformed `srcset` values or fall back to unexpected behavior, resulting in the wrong image being loaded — potentially hurting performance by downloading unnecessarily large files or degrading visual quality by selecting a too-small image. Third, standards-compliant markup ensures consistent, predictable behavior across all browsers and devices.
A common mistake is specifying a plain URL without any descriptor, or mixing density descriptors (`1x`, `2x`) with the `sizes` attribute. An image candidate string without any descriptor defaults to `1x`, which is a density descriptor — and that conflicts with the presence of `sizes`.
## Examples
### ❌ Incorrect: Missing width descriptor with `sizes` present
```html
```
Here, `image-small.jpg` has no width descriptor. Since `sizes` is present, this triggers the validation error.
### ❌ Incorrect: Using density descriptors with `sizes`
```html
```
Density descriptors (`1x`, `2x`) are incompatible with the `sizes` attribute.
### ✅ Correct: All candidates have width descriptors
```html
```
Every image candidate now includes a width descriptor, which pairs correctly with the `sizes` attribute.
### ✅ Correct: Using density descriptors without `sizes`
If you want to use density descriptors instead of width descriptors, simply remove the `sizes` attribute:
```html
```
This is valid because density descriptors don't require (and shouldn't be used with) the `sizes` attribute.
### ✅ Correct: Width descriptors on `` with `sizes`
```html
```
Each entry in `srcset` specifies its intrinsic width, and `sizes` tells the browser which display width to expect at each breakpoint. The browser then selects the best-fitting image automatically.
```
Density descriptors (`1x`, `2x`) are incompatible with the `sizes` attribute.
### ✅ Correct: All candidates have width descriptors
```html
```
Each entry in `srcset` specifies its intrinsic width, and `sizes` tells the browser which display width to expect at each breakpoint. The browser then selects the best-fitting image automatically.