import { Dimensions } from "react-native";
const win = Dimensions.get('window');
<Image style={{ width: win.width/2, height: win.width/2, resizeMode: "contain", alignSelf: "center", borderWidth: 1, borderRadius: 20, }} source={{uri:'https://facebook.github.io/react/img/logo_og.png'}} resizeMode="stretch"
/>

 flex: 1, width: 50, height: 50, resizeMode: 'contain' 

image : {	width : null,	resizeMode : 'contain',	height : 220	}

	flex: 1, width: 50, height: 50, resizeMode: 'contain' 

First import Dimensions from react-native
import { Dimensions } from 'react-native';
then you have to get the dimensions of the window
const win = Dimensions.get('window');
Now calculate ratio as
const ratio = win.width/541; //541 is actual image width
now the add style to your image as
imageStyle: { width: win.width, height: 362 * ratio, //362 is actual height of image
}