The calculated distance (air line) between Poulton-le-Fylde and Birkenhead is approximately 30 miles respectively 49 kilometers.
By car or train, the actual journey to Birkenhead is certainly longer, as only the direct route (as the crow flies) between Poulton-le-Fylde and Birkenhead has been calculated here.
Air line (approximately)
49 kilometers
26 nautical miles