React Native Responsive Font Size

I would like to ask how react native handle or do the responsive font. For example in iphone 4s i Have fontSize: 14, while in iphone 6 I have fontSize: 18.

You can use PixelRatio

For example:

var React = require('react-native');

var {StyleSheet, PixelRatio} = React;

var FONT_BACK_LABEL   = 18;

if (PixelRatio.get() <= 2) {
  FONT_BACK_LABEL = 14;
}

var styles = StyleSheet.create({
  label: {
    fontSize: FONT_BACK_LABEL
  }
});

Edit:

Another example:

import { Dimensions, Platform, PixelRatio } from 'react-native';

const {
  width: SCREEN_WIDTH,
  height: SCREEN_HEIGHT,
} = Dimensions.get('window');

// based on iphone 5s's scale
const scale = SCREEN_WIDTH / 320;

export function normalize(size) {
  const newSize = size * scale 
  if (Platform.OS === 'ios') {
    return Math.round(PixelRatio.roundToNearestPixel(newSize))
  } else {
    return Math.round(PixelRatio.roundToNearestPixel(newSize)) - 2
  }
}

Usage:

fontSize: normalize(24)

You can go one step further by allowing sizes to be used on every <Text /> components by pre-defined sized.

Example:

const styles = {
  mini: {
    fontSize: normalize(12),
  },
  small: {
    fontSize: normalize(15),
  },
  medium: {
    fontSize: normalize(17),
  },
  large: {
    fontSize: normalize(20),
  },
  xlarge: {
    fontSize: normalize(24),
  },
};

We use a simple, straight-forward, scaling utils functions we wrote:

import { Dimensions } from 'react-native';
const { width, height } = Dimensions.get('window');

//Guideline sizes are based on standard ~5" screen mobile device
const guidelineBaseWidth = 350;
const guidelineBaseHeight = 680;

const scale = size => width / guidelineBaseWidth * size;
const verticalScale = size => height / guidelineBaseHeight * size;
const moderateScale = (size, factor = 0.5) => size + ( scale(size) - size ) * factor;

export {scale, verticalScale, moderateScale};

Saves you some time doing many ifs. You can read more about it on my blog post.

---

Edit: I thought it might be helpful to extract these functions to their own npm package, I also included ScaledSheet in the package, which is an automatically scaled version of StyleSheet. You can find it here: react-native-size-matters.

adjustsFontSizeToFit and numberOfLines works for me. They adjust long email into 1 line.

<View>
  <Text
    numberOfLines={1}
    adjustsFontSizeToFit
    style={{textAlign:'center',fontSize:30}}
  >
    {this.props.email}
  </Text>
</View>

Because responsive units aren't available in react-native at the moment, I would say your best bet would be to detect the screen size and then use that to infer the device type and set the fontSize conditionally.

You could write a module like:

function fontSizer (screenWidth) {
  if(screenWidth > 400){
    return 18;
  }else if(screenWidth > 250){
    return 14;
  }else { 
    return 12;
  }
}

You'll just need to look up what the default width and height are for each device. If width and height are flipped when the device changes orientation you might be able to use aspect ratio instead or just figure out the lesser of the two dimensions to figure out width.

This module or this one can help you find device dimensions or device type.

I managed to overcome this by doing the following.

1. Pick the font size you like for the current view you have (Make sure it looks good for the current device you are using in the simulator).

2. import { Dimensions } from 'react-native' and define the width outside of the component like so: let width = Dimensions.get('window').width;

3. Now console.log(width) and write it down. If your good looking font size is 15 and your width is 360 for example, then take 360 and divide by 15 ( = 24). This is going to be the important value that is going to adjust to different sizes.

   Use this number in your styles object like so: textFontSize: { fontSize = width / 24 },...

Now you have a responsive fontSize.

Take a look at the library I wrote: https://github.com/tachyons-css/react-native-style-tachyons

It allows you to specify a root-fontSize (rem) upon start, which you can make dependent of your PixelRatio or other device-characteristics.

Then you get styles relative to your rem, not only fontSize, but paddings etc. as well:

<Text style={[s.f5, s.pa2, s.tc]}>
     Something
</Text>

Expanation:

• f5is always your base-fontsize
• pa2 gives you padding relative to your base-fontsize.

import { Dimensions } from 'react-native';

const { width, fontScale } = Dimensions.get("window");

const styles = StyleSheet.create({
    fontSize: idleFontSize / fontScale,
});

fontScale get scale as per your device.

I simply use the ratio of the screen size, which works fine for me.

const { width, height } = Dimensions.get('window');

// Use iPhone6 as base size which is 375 x 667
const baseWidth = 375;
const baseHeight = 667;

const scaleWidth = width / baseWidth;
const scaleHeight = height / baseHeight;
const scale = Math.min(scaleWidth, scaleHeight);

export const scaledSize =
    (size) => Math.ceil((size * scale));

Test

const size = {
    small: scaledSize(25),
    oneThird: scaledSize(125),
    fullScreen: scaledSize(375),
};

console.log(size);

// iPhone 5s
{small: 22, oneThird: 107, fullScreen: 320}
// iPhone 6s
{small: 25, oneThird: 125, fullScreen: 375}
// iPhone 6s Plus
{small: 28, oneThird: 138, fullScreen: 414}

We can use flex layout and use adjustsFontSizeToFit={true} for responsive font sizes.And the text would adjust according to the size of the container.

     <Text
    adjustsFontSizeToFit
    style={styles.valueField}>{value}
    </Text>

But in styles you need to put a fontsize as well only then will adjustsFontSizeToFit work.

    valueField: {
    flex: 3,
    fontSize: 48,
    marginBottom: 5,
    color: '#00A398',
},

I recently ran into this problem and ended up using react-native-extended-stylesheet

You can set you rem value and additional size conditions based on screen size. As per the docs:

// component
const styles = EStyleSheet.create({
  text: {
    fontSize: '1.5rem',
    marginHorizontal: '2rem'
  }
});
// app entry
let {height, width} = Dimensions.get('window');
EStyleSheet.build({
  $rem: width > 340 ? 18 : 16
});

Why not using PixelRatio.getPixelSizeForLayoutSize(/* size in dp */);, it's just the same as pd units in Android.

I'm usually using this :

import React from 'react';
import { View, Text, StyleSheet, Dimensions } from 'react-native';

var heightY = Dimensions.get("window").height;

export default function App() {
  return (
    <View style={styles.container}>
      <Text style={styles.textStyle}>fontSize {heightY * 0.014}</Text>
    </View>
  )
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: '#fff',
    alignItems: 'center',
    justifyContent: 'center',
  },
  textStyle: {
    fontSize: heightY * 0.014,
  }
})

The idea is to get the fontSize depending on height of your screen. Example calculation:

// Height 785,.. -> fontSize = 11 
// Height 1000 -> fontSize = 14
// Height 1285,.. -> fontSize = 18

You can also try using this if you want it to depend on your screen width:

var widthX = Dimensions.get("window").width;

Need to use this way I have used this one and it's working fine.

react-native-responsive-screen npm install react-native-responsive-screen --save

Just like I have a device 1080x1920

The vertical number we calculate from height **hp**
height:200
200/1920*100 = 10.41% - height:hp("10.41%")


The Horizontal number we calculate from width **wp**
width:200
200/1080*100 = 18.51% - Width:wp("18.51%")

It's working for all device

A slightly different approach worked for me :-

const normalize = (size: number): number => {
  const scale = screenWidth / 320;
  const newSize = size * scale;
  let calculatedSize = Math.round(PixelRatio.roundToNearestPixel(newSize))

  if (PixelRatio.get() < 3)
    return calculatedSize - 0.5
  return calculatedSize
};

Do refer Pixel Ratio as this allows you to better set up the function based on the device density.

You can use something like this.

var {height, width} = Dimensions.get('window'); var textFontSize = width * 0.03;

inputText: {
	color : TEXT_COLOR_PRIMARY,
	width: '80%',
	fontSize: textFontSize
}

Hope this helps without installing any third party libraries.