The calculated distance (air line) between Grodzisk Mazowiecki and Bydgoszcz is approximately 131 miles respectively 210 kilometers.
By car or train, the actual journey to Bydgoszcz is certainly longer, as only the direct route (as the crow flies) between Grodzisk Mazowiecki and Bydgoszcz has been calculated here.
Air line (approximately)
210 kilometers
114 nautical miles