How capital ships retained reserve buoyancy

How much reserve buoyancy did battleships and battlecruisers usually have?

The usual standard was for the intact armored citadel to provide sufficient buoyancy; a half-citadel standard was exceptionally demanding.

The armored citadel was the central design criterion for capital-ship reserve buoyancy. As long as that protected volume remained intact, it needed to provide enough buoyancy to keep the vessel afloat. A stricter standard based on retaining only half the citadel is mentioned as a design aspiration. The required subdivision and volume would probably make that standard impractical.