Spain’s recent banning of models with Body Mass Indexes (BMIs) under 18 means the country’s most famous face, Esther Canadas , who reportedly has a BMI of 14, wouldn’t be able to walk the runway. Other models who won’t be gracing Madrid’s catwalks anytime soon include: Kate Moss (BMI 16.1), Gisele Bundchen (BMI 16) and Naomi Campbell (BMI 16.5).

BMI, a number derived from plugging height and weight into an equation, is considered “a reliable indicator of body fatness,” says the Centers for Disease Control Web site.

Would you make the cut? Here’s how to figure out yours:

Weight in pounds/height in inches(squared) * 703 = BMI

Federal guidelines dictate that a BMI under 18.5 indicates the individual is underweight; 18.5-24.9 is normal; 25-29.9 is overweight; and 30 and above is obese.