P45
P45 may refer to:

 Bell P-39 Airacobra (originally P-45), a fighter produced by Bell Aircraft for the U.S. Army Air Forces during World War II
 Intel P45, a mainstream desktop computer chipset
 P 45, a state regional road in Latvia
 P45, a digital camera back made by the Danish company Phase One
 P45 (tax), the reference code of a document titled Details of employee leaving work
 P45 road (Ukraine), a regional Ukraine road in Sumy Oblast and Kharkiv Oblast
 Papyrus 45 (also 45), an early New Testament manuscript
 Pneumonoultramicroscopicsilicovolcanoconiosis, a synonym for the disease known as silicosis

See also
 Ferrari P4/5 by Pininfarina, a one-off sports car made by Italian sports car manufacturer Ferrari