The best replacement for density is specific gravity.

The best alternatives to density are rated as following:
★★★★★  specific gravity
★★★  mass
★★★  temperature
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★★  pressure
★  weight
★  concentration
★  low density memory
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★  distribution
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★  air
★  buoyancy
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  specific weight
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Your alternative for density is not listed? Suggest!
Speaking about density, one probably shouldn't forget about mass and volume.

Other search terms related to density and their ratings are:
★★★★★ mass and volume
★★★★ liquids
★★★★ mass
★★★★ volume
★★★★ ideal gas law
★★★ specific gravity
★★★ water displacement
★★ gas laws
★ molar mass
pressure
changing volume
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density
specific gravity
mass