In more detail
The Mosteller formula is √(height (cm) × weight (kg) / 3600); the older DuBois formula is 0.007184 × weight^0.425 × height^0.725. For 175 cm and 70 kg they give 1.84 and 1.85 m². Most adults fall roughly between 1.6 and 2.2 m², and kidney function results are scaled to a reference of 1.73 m² (see GFR (glomerular filtration rate)). Several other formulas exist, some designed specifically for children.
Why it matters
Many chemotherapy doses, and some other medicines, are prescribed per square metre because BSA follows metabolic and organ size more closely than weight alone. Cardiac output divided by BSA gives the cardiac index. The formulas can disagree by a few per cent, more at extremes of height and weight, so one method should be used consistently; dosing decisions belong to the prescribing team.
Example
Mosteller: √(175 × 70 / 3600) = √3.4028 = 1.84 m²
DuBois: 0.007184 × 70^0.425 × 175^0.725 = 1.85 m²
Dose prescribed at 75 mg/m²: 75 × 1.84 = 138 mg