The amount of protein in a soy protein powder largely depends on how refined the product is. For best results, you should seek a "soy protein isolate" as isolates generally contain at least 90% protein content. To check the protein content of your product you can review the "nutritional facts" label. The protein content per serving in grams as compared to the total grams per serving will reveal to you just how pure your soy protein powder is.
Example:
Serving Size 24g
Fat 0.5g
Sodium 200mg
Carbohydrate < 0.5g
Protein 20g
To work out the protein content as a percentage, we divide the protein content by the serving size and then multiply by 100.
20g (protein) ÷ 24g (serving size) × 100 = 83.3%