O₂ content is the truest measure of oxygen present but is difficult to measure directly and so is normally estimated from the other values.

Calculating O₂ content

When fully saturated, 1 g of Hb holds 1.34 mL O₂. Assuming a Hb concentration of 150 g/L (15 g/dL), it is possible to calculate the oxygen content in arterial blood (C_aO₂):

C_aO₂= Hb-bound + dissolved

      = ([Hb] x 1.34 x satn) + (0.23 x PO₂)

      = (150 x 1.34 x 0.98) + (0.23 x 13)

      = 197 + 3

      = 200 mL/L