Japan holds the record for the smallest rocket to reach orbit with the SS-520, which put a cubesat into orbit in 2018. Its dimensions according to Wikipedia:

Japan holds the record for the smallest rocket to reach orbit with the SS-520, which put a cubesat into orbit in 2018. Its dimensions according to Wikipedia: Height – 31 feet (9.54 meters) Weight – 2.9 tons (2.6 metric tons) Diameter – 20 inches (52 centimeters) Payload to Low-Earth Orbit – ~9 lbs (4 kg)