The calculated distance (air line) between Sing Buri and Krathum Baen is approximately 86 miles respectively 138 kilometers.
By car or train, the actual journey to Krathum Baen is certainly longer, as only the direct route (as the crow flies) between Sing Buri and Krathum Baen has been calculated here.
Air line (approximately)
138 kilometers
75 nautical miles