To determine your RDA for protein, you can multiply your weight in pounds by 0.36, or use this online protein calculator. For a 50-year-old woman who weighs 140 pounds woman and who is sedentary (doesn’t exercise), that translates into 53 grams of protein a day.he Recommended Dietary Allowance (RDA) for protein is a modest 0.8 grams of protein per kilogram of body weight. The RDA is the amount of a nutrient you need to meet your basic nutritional requirements.