Protein (g a day) = body weight in kg (pounds × 0.4536) × the g per kg range for your activity: 0.8 (RDA), 1.0 to 1.2 over age 65, 1.4 to 2.0 with regular exercise, 1.6 to 2.2 for strength training, 2.3 to 3.1 for strength training in a calorie deficit. The result shows the low end of the range.
The number shown is grams of protein a day at the low end of the published range for the activity level you picked, with the full range in the note. It is a planning figure for healthy adults, not a prescription, and each range comes from a different source with its own purpose.
The RDA of 0.8 g per kg is a floor. It comes from a meta-analysis of nitrogen balance studies that put the median requirement at 0.65 g per kg and set the RDA at about 0.83 g per kg to cover nearly all healthy adults. It is meant to prevent shortfall, not to describe an ideal intake for muscle. The meta-analysis found no clear difference by sex, age group or climate, though women showed a hint of a lower requirement.
The higher ranges answer different questions. The ISSN gives 1.4 to 2.0 g per kg for most exercising people and 2.3 to 3.1 g per kg to keep lean mass during a calorie deficit. A meta-analysis of strength training trials found no further muscle gain on average above about 1.6 g per kg. PROT-AGE advises at least 1.0 to 1.2 g per kg for adults over 65.
Body weight drives the arithmetic, since every range is per kilogram. The calculator uses total body weight, as the cited sources do, so the same g per kg figure gives a larger number for a heavier person whatever their build.
Age shifts the need. PROT-AGE says older adults need more protein than younger adults to offset changes in how the body handles it, and the strength training meta-analysis found the extra muscle gain from added protein shrank with increasing age. Training history works the other way, since added protein was more effective in people already resistance trained.
Health changes the picture most. The PROT-AGE and ESPEN groups both advise 1.2 to 1.5 g per kg for older adults with acute or chronic illness. People with severe kidney disease, an eGFR below 30 and not on dialysis, are the stated exception and may need to limit protein. A calorie deficit raises the range in the ISSN position.
Recalculate after a lasting change in body weight, after a change in training, such as starting a strength program or a diet phase, and on reaching 65, when the older adult ranges begin to apply. A new diagnosis that affects the kidneys or liver is also a reason to revisit the number with a clinician, since the healthy adult ranges may no longer fit.
There is no blood test for protein intake itself. BUN can rise with a higher protein intake and is read alongside creatinine, while albumin and total protein depend on liver function, hydration and inflammation more than on recent meals. Anyone with reduced kidney function, or a result on those markers outside the lab range, is best served by a conversation with a clinician or registered dietitian before raising intake.
Every range here was built in healthy adults. The RDA meta-analysis drew on 235 people across 19 studies, and the strength training meta-analysis pooled 49 trials with 1,863 participants. None of these sources set ranges for pregnancy, children or people with kidney or liver disease.
The ranges are averages with wide spread between people. The 1.6 g per kg breakpoint is an average from trials, and its upper confidence limit reached 2.2, so some people may gain at higher intakes and others at lower. Using total weight also ignores body composition, so the figure can read high for someone carrying a lot of body fat. Treat the number as a starting point to discuss with a clinician or dietitian.
Take someone who weighs 180 lb and picks Exercise regularly. The calculator converts pounds to kilograms, 180 × 0.4536, which gives 81.6 kg. It then multiplies by the ISSN range for most exercising adults. 81.6 × 1.4 is 114 g a day and 81.6 × 2.0 is 163 g a day. The result shows 114 g, the low end, with the 114 to 163 g range in the note.
The same person at the RDA of 0.8 g per kg would see 65 g a day. Choosing Strength training to build muscle gives 131 to 180 g, from 1.6 and 2.2 g per kg. The calorie deficit option gives 188 to 253 g from 2.3 and 3.1 g per kg. At 65 or older, the PROT-AGE range of 1.0 to 1.2 gives 82 to 98 g.
Seen side by side, the published ranges for one body span from 65 g to 253 g a day. The activity choice matters more than small changes in weight, so pick the option that matches a typical week rather than the best one.
The RDA and the sports ranges come from different methods. The RDA rests on nitrogen balance, which measures whether the body is losing protein. The ISSN ranges and the meta-analysis breakpoint come from studies of muscle gain and lean mass retention in exercising people, which is why they sit higher. Neither approach is wrong. They answer different questions about the same nutrient.
For older adults, two expert groups agree. PROT-AGE and ESPEN both recommend at least 1.0 to 1.2 g per kg a day for healthy older people, and both raise it with illness. Some guidance frames protein as a share of total calories instead, and the ISSN notes its range falls within the acceptable intake range published by the Institute of Medicine. Per kilogram figures are easier to apply to one person, which is why this calculator uses them.
The FitScript Baseline panel measures the values this calculator uses. Related: total protein, albumin, bun.
For healthy adults, at least 0.8 g per kg of body weight. Exercising adults are usually advised 1.4 to 2.0 g per kg, and adults over 65 at least 1.0 to 1.2 g per kg.
In a meta-analysis of strength training trials, intakes above about 1.6 g per kg a day added no further muscle on average.
The PROT-AGE group recommends at least 1.0 to 1.2 g per kg a day for adults over 65, and 1.2 or more for those who exercise.