Basal metabolic rate scales as B ∝ M^(3/4) across 27 orders of magnitude of body mass — from mitochondria to blue whales. West, Brown & Enquist (1997) derive the 3/4 exponent from fractal vascular networks.
log B = log B₀ + β·log M | β = 3/4 (Kleiber 1932; West-Brown-Enquist 1997)