# getRootFontSize

> Read the document root's computed font-size in pixels. Used internally by `resolveCssSize` to convert rem-based values to px.

Source: https://ngwr.dev/reference/utils/get-root-font-size  
Kind: Util

## Usage

```angular-ts
import { getRootFontSize } from 'ngwr/utils';

const px = getRootFontSize();   // e.g. 16
const remToPx = 2 * px;          // convert '2rem' to pixels

// The fallback is what SSR (and an unparseable computed value) resolves to.
const px14 = getRootFontSize(14);
```

## Why ngwr provides this

There's no built-in way to read the root font-size in TS — the recipe (`parseFloat(getComputedStyle(document.documentElement).fontSize)`) is verbose, easy to mistype (people often grab `body` instead of `documentElement`), and crashes during SSR where `document` is undefined. ngwr wraps it once, SSR-safely.

```angular-ts
// Native — verbose, easy to typo `body` instead of `documentElement`,
// and crashes on SSR where `document` is undefined.
const px = parseFloat(getComputedStyle(document.documentElement).fontSize);

// ngwr — one call, SSR-safe (returns a sensible 16 when document isn't available).
const px = getRootFontSize();
```

## API

| Name | Description | Type | Default |
| --- | --- | --- | --- |
| `getRootFontSize(fallback?)` | Pixel value of `:root` font-size. Useful for converting rem-based inputs to px in TS. `fallback` is returned when there is no DOM (SSR) or the computed value does not parse. | `(fallback = 16) => number` | `—` |