The clothing size for a woman with a 36-inch waist will vary depending on where they shop and what type of clothing it pertains to, but with the ASOS brand, a 36-inch waist could mean a US size 14 in the curve size guide or a US size 4 in the maternity size guide. Some brands, like American Eagle, don't offer clothes that fit a 36-inch waist.
A 36-inch waist is generally regarded as an XL size, but most clothing types, especially dresses, require other measurements to be known, like the bust and hip measurements. Skirts, as well, require other measurements to determine the right size, particularly the hip measurement.
For ASOS clothes, they offer a petite, curve and maternity size rating system. These sizes are originally listed in U.K. form, so they must be converted to their U.S. equivalents. In general, any U.K. size provided by the ASOS brand is simply four more than the U.S. version. There are no sizes in the petite section for 36-inch waist measurements but the curve and maternity size listings do. Because of this, the size descriptions tend to vary somewhat between brands, as some brands don't even offer clothes that fit a 36-inch waist.