504 (disambiguation)

504 may refer to:
 * 504, a year
 * Avro 504, a World War 1 era biplane aircraft built by Avro
 * Peugeot 504, a large family car
 * Area code 504, telephone code in Louisiana, United States
 * Section 504 of the Rehabilitation Act, which protects Americans with disabilities from discrimination by any entity that receives Federal funding
 * 504 Gateway Timeout, a server error in web browsing etc. – see List of HTTP status codes § Server errors
 * 504 King, a streetcar route in Toronto, Canada
 * No. 504 Squadron RAF, of Britain's Royal Air Force