# Bad value X for attribute “width” on element “img”: Expected a digit but saw “N” instead.

> Canonical HTML version: https://rocketvalidator.com/html-validation/bad-value-x-for-attribute-width-on-element-img-expected-a-digit-but-saw-n-instead
> Attribution: Rocket Validator (https://rocketvalidator.com)
> License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

The `width` of an `<img>` holds the text `NaN`, which usually means a script or template calculated the size from a missing or non-numeric value.

The `width` attribute takes a non-negative integer: digits only. `NaN` ("not a number") is what JavaScript returns when arithmetic runs on `undefined` or a non-numeric string, for example `Math.round(data.width * scale)` when `data.width` is missing. Writing that result into the markup puts the literal text `NaN` in the attribute. Other words that start with that letter, such as `null` or `none`, trigger the same message with a lowercase `n`.

Browsers can't read a number from `NaN`, so they ignore the attribute. The image then gets no reserved space before it loads, and the content below it shifts once it arrives. The `height` attribute often has the same bug and gets its own error.

Fix the code that produces the value. Check that the number is finite before you write it (`Number.isFinite(width)` in JavaScript), and leave the attribute out when the size isn't known.

## Invalid example

```html
<img src="photo.jpg" alt="A red car" width="NaN" height="NaN">
```

## Valid example

```html
<img src="photo.jpg" alt="A red car" width="640" height="480">
```