Normalize RN styles - Code for iPhone 6s and it should work across all devices.

normalizeRNStyles.js

import _ from 'lodash'
import { Dimensions } from 'react-native'
const { height } = Dimensions.get('window')
const iphone6Height = 667

const fieldsToNormalize = [
  'fontSize',
  'width',
  'height',
  'margin',
  'marginTop',
  'marginBottom',
  'marginLeft',
  'marginRight',
  'padding',
  'paddingTop',
  'paddingBottom',
  'paddingLeft',
  'paddingRight',
]

const normalizeFont = (size) => {
  let newSize = size
  if (height === 568) {
    newSize = size * (1 / 1.2)
  } else if (height === 667) {
    newSize = size
  } else if (height === 736) {
    newSize = size * (1.4 / 1.2)
  }
  return newSize
}

const normalizeValue = (styleKey, value) => {
  if (styleKey === 'fontSize') {
    return normalizeFont(value)
  }
  return (height / iphone6Height) * value
}

function normalizeStyle(style) {
  const normalizedStyle = _.mapValues(_.pick(style, fieldsToNormalize), (value, key) => normalizeValue(key, value))
  return {
    ..._.omit(style, fieldsToNormalize),
    ...normalizedStyle
  }
}

export default function normalizeStyles(styles) {
  return _.mapValues(styles, (style) => normalizeStyle(style))
}