JAVASCRIPT

react native scaling font

<Text
    numberOfLines={1}// add this
    adjustsFontSizeToFit// add this
    style={{textAlign:'center',fontSize:30}}
  >

react native responsive font

import { Dimensions } from 'react-native';

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

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

responsive font size react native

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

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

export function normalize(size, multiplier = 2) {
  const scale = (width / height) * multiplier;

  const newSize = size * scale;

  return Math.round(PixelRatio.roundToNearestPixel(newSize));
}