import { useDimensions } from 'react-dimensions-hook';

function MyComponent() {
  const { ref, dimensions } = useDimensions();

  return (
    <div
      ref={ref}
      style={{
        width: '500px',
        height: '100px',
        margin: '0 auto'
      }}
    >
      my size is {dimensions.width} × {dimensions.height}
    </div>
  );
}