Western white pine is a medium- to large-sized tree that can grow up to 60 metres high and two metres in diameter. It is usually found in closed groups of trees and has a sparse crown and short branches. When the tree is young, its bark is thin, smooth and greyish-green, and it turns darker as the tree ages, forming deep, vertical grooves with small rectangular scaly plates.
Needles occur in bunches of five, about 5 to 10 centimetres long. Slender, straight and soft to touch, they are bluish-green in colour with a whitish tinge. The edges are very finely toothed. Seed cones are cylindrical when closed, about 10 to 25 centimetres long, and they are on a two-centimetre stalk. The scales are often bent backwards when dry. The seeds have wings about three centimetres long.