All three of the Olympic-class ships had eleven decks, eight of which were for passenger use. From top to bottom, the decks were:
- The Boat Deck, on which the lifeboats were positioned. The bridge and wheelhouse were at the forward end, in front of the captain's and officers' quarters. The bridge stood 8 feet (2.4 m) above the deck, extending out to either side so that the ship could be controlled while docking. The wheelhouse stood directly behind and above the bridge. The entrance to the First Class Grand Staircase and gymnasium were located midships along with the raised roof of the First Class lounge, while at the rear of the deck were the roof of the First Class smoke room and the relatively modest Second Class entrance. The wood-covered deck was divided into four segregated promenades; for officers, First Class passengers, engineers and Second Class passengers respectively. Lifeboats lined the side of the deck except in the First Class area, where there was a gap so that the view would not be spoiled.
- A Deck, also called the Promenade Deck, extended along the entire 546 feet (166 m) length of the superstructure. It was reserved exclusively for First Class passengers and contained First Class cabins, the First Class lounge, smoke room, reading and writing rooms and Palm Court.
- B Deck, the Bridge Deck, was the top weight-bearing deck and the uppermost level of the hull. More First Class passenger accommodation was located here with six palatial staterooms (cabins) featuring their own private promenades. Both were run by subcontracted chefs and their staff; all were lost in the disaster. The Second Class smoking room and entrance hall were both located on this deck. The raised forecastle of the ship was forward of the Bridge Deck, accommodating Number 1 hatch (the main hatch through to the cargo holds), various pieces of machinery and the anchor housings. It was kept off-limits to passengers. Aft of the Bridge Deck was the raised Poop Deck, 106 feet (32 m) long, used as a promenade by Third Class passengers. The forecastle and Poop Deck were separated from the Bridge Deck by well decks [A well deck is an exposed deck (weather deck) lower than decks fore and aft.].
- C Deck, the Shelter Deck, was the highest deck to run uninterrupted from the ships' stem to stern. It included the two well decks; the aft one served as part of the Third Class promenade. Crew cabins were located under the forecastle and Third Class public rooms were situated under the Poop Deck. In between were the majority of First Class cabins and the Second Class library.
- D Deck, the Saloon Deck, was dominated by three large public rooms – the First Class Reception Room, the First Class Dining Saloon and the Second Class Dining Saloon. An open space was provided for Third Class passengers. First, Second and Third Class passengers had cabins on this deck, with berths for firemen located in the bow. It was the highest level reached by the ships' watertight bulkheads (though only by eight of the fifteen bulkheads).
- E Deck, the Upper Deck, was predominantly used for passenger accommodation for all classes plus berths for cooks, seamen, stewards and trimmers. Along its length ran a long passageway nicknamed Scotland Road by the crew, in reference to a famous street in Liverpool.
- F Deck, the Middle Deck, was the last complete deck and mainly accommodated Third Class passengers. There were also some Second Class cabins and crew accommodation. The Third Class dining saloon was located here, as were the swimming pool and Turkish bath.
- G Deck, the Lower Deck, was the lowest complete deck that carried passengers, and had the lowest portholes, just above the waterline. The squash court was located here along with the travelling post office where mail clerks sorted letters and parcels so that they would be ready for delivery when the ship docked. Food was also stored here. The deck was interrupted at several points by orlop (partial) decks over the boiler, engine and turbine rooms.
- The Orlop decks and the Tank Top were at the lowest level of the ship, below the waterline. The orlop decks were used as cargo space, while the Tank Top – the inner bottom of the ship's hull – provided the platform on which the ship's boilers, engines, turbines and electrical generators sat. This part of the ship was dominated by the engine and boiler rooms, areas that passengers would never normally see. They were connected with higher levels of the ship by flights of stairs; twin spiral stairways near the bow gave access up to D Deck.