The capillary length λ_c sets the scale at which surface tension and gravity are comparable. For water: λ_c ≈ 2.7 mm. Objects smaller than λ_c can float on water surface tension. Capillary rise (Jurin's Law) balances surface tension lifting force 2πrγcos(θ) against weight πr²hρg. Negative curvature (θ > 90°) gives capillary depression (mercury in glass).