You can calculate exactly how much weight you’ll lose using a calorie calculator .
Insert your information and figure your daily calorie expenditure. Multiple this number by 30, and then divide it by 3,500 as that is how much of a deficit you need to be in, in order to lose 1lb of body fat.
For example a man that burns 2,000 calories a day would expect to be in a deficit of 60,000 during a 30 day fast, divide that number by 3,500, and he can expect to lose 17 lbs.
What’s going to happen after those 30 days? You’ll put all the weight back on because you’ll be extremely hungry once you start eating again. A 30 day fast is great for autophagy and/or spirituality but for weight loss? Probably not ideal.
Have you even done fasting before with any success? You’re better off starting with some 48 or 72 hour fasts with refeeds.
Are you a woman by any chance? 140lbs doesn’t sound very healthy for someone of 6’1 height.