The short answer
Sedentary adults need about 0.8 g of protein per kg of bodyweight. If you train, 1.4 to 2.0 g per kg is the supported range, and if you are losing fat, aim toward 1.8 to 2.7 g per kg. For an 80 kg person losing fat that is roughly 176 g per day.
The RDA is a floor, not a target
The 0.8 g per kg figure that appears on nutrition labels and in general health advice is the Recommended Dietary Allowance. It was set to be the amount that prevents deficiency in almost all healthy, sedentary adults.
Read that carefully, because it is the source of most confusion about protein. It answers "how little can someone eat without becoming deficient", not "how much supports muscle, satiety and body composition". Those are different questions with different answers, and the second one has a substantial body of research behind it.
If you lift, run, are in a calorie deficit, or are past middle age and trying to hold on to lean tissue, 0.8 g per kg is not where you should be.
What the research supports
| Situation | Grams per kg of bodyweight | For an 80 kg person |
|---|---|---|
| Sedentary, general health | 0.8 (RDA) | 64 g |
| Active, maintaining weight | 1.4 to 1.8 | 112 to 144 g |
| Building muscle | 1.6 to 2.2 | 128 to 176 g |
| Losing fat while training | 1.8 to 2.7 | 144 to 216 g |
The 1.4 to 2.0 g per kg band for active individuals comes from the International Society of Sports Nutrition position stand on protein and exercise. Note that it is expressed per kilogram of bodyweight, not as a percentage of calories, and that matters: a percentage rule would lower your protein target every time you cut calories, which is exactly backwards.
The fat loss row sits highest for two reasons. Protein spares lean tissue when energy is short, so more of what you lose comes from fat. And it is the most satiating of the three macronutrients, which makes a deficit meaningfully easier to sustain than the same calories arranged differently.
The lean mass refinement
If you supply a body fat percentage, the calculator adds a second figure based on fat-free mass rather than total weight, using the range from Helms et al. (2014): 2.3 to 3.1 g per kg of lean mass for athletes in a deficit.
Two things about that number are worth stating plainly, because they are routinely misquoted.
It is per kilogram of lean mass, not bodyweight. Applying 2.3 to 3.1 to total weight would produce a wildly inflated target for anyone carrying meaningful body fat. This is why the row only appears once you provide a body fat figure, rather than being offered as a default.
It was derived in lean, resistance-trained athletes. The population studied was already close to competition condition. If you are starting a fat loss phase from a higher body fat percentage, you are further from that population, and the bodyweight-based range above is the more appropriate reference.
If you do not know your body fat percentage, the body fat calculator estimates it from tape measurements.
Distribution matters less than the total
A recurring worry is timing: whether protein needs to be split evenly, whether there is an anabolic window, whether the body can only use 30 g at a sitting.
The honest answer is that the daily total does most of the work. Spreading protein across three or four meals is a reasonable default and probably marginally better than one large serving, mainly because it is easier to eat that way. But someone hitting their target across two meals is in a far better position than someone with a perfect distribution who falls 40 g short.
Get the total right first. Optimise the arrangement afterwards, if at all.
Why the target usually gets missed
Protein is the macronutrient people most often intend to hit and most often do not. The reason is almost never a lack of knowledge about the number.
It is that protein content is not obvious by eye. Two similar looking meals can differ by 30 g. Unless you are tracking, you learn at the end of the day that you fell short, at which point the day is over. Most people discover they were running 30 to 50 g under only after they start measuring.
CalAlly makes measuring take almost no time. Describe the meal out loud, the AI breaks it into ingredients and returns the protein along with everything else, one tap logs it, about 3 seconds. The running total is visible during the day rather than after it, which is the difference between correcting a shortfall and merely noticing one.