What this calculator does
Measuring protein loss properly once meant collecting every drop of urine for 24 hours, which patients find difficult and frequently get wrong. The protein-to-creatinine ratio on a single sample estimates the same figure.
It works because creatinine is excreted at a roughly steady rate of about 1 gram a day. Dividing protein by creatinine in the same sample therefore approximates grams of protein per day directly: a ratio of 3.50 estimates 3.50 g/day.
The formula
Divide urine protein by urine creatinine, both in mg/dL. The result approximates daily protein excretion in grams, on the assumption of roughly 1 gram of creatinine excreted per day.
| Term | Meaning |
|---|---|
| Protein-to-creatinine ratio | Urine protein divided by urine creatinine from one sample. |
| Nephrotic range | Above roughly 3 to 3.5 g/day, a threshold with specific clinical meaning. |
| Spot sample | A single urine specimen rather than a timed collection. |
The inputs explained
| Field | What to enter |
|---|---|
| Urine protein (mg/dL) | Urine protein in mg/dL. |
| Urine creatinine (mg/dL) | Urine creatinine in mg/dL, from the same sample. |
When to use it
Screening for proteinuria
A spot sample is far more practical than a 24 hour collection and is now standard.
Monitoring kidney disease
Repeated ratios track whether protein loss is worsening or improving.
Avoiding a timed collection
Incomplete 24 hour collections are common and produce misleading results.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What does each protein level estimate?
The same creatinine at three protein levels.
| Urine protein | Estimated 24-hour protein excretion | Reference |
|---|---|---|
| 10 mg/dL | 0.10 g/day | Normal is typically under about 0.2 g/day; nephrotic-range proteinuria is above 3 to 3.5 g/day |
| 30 mg/dL | 0.30 g/day | Normal is typically under about 0.2 g/day; nephrotic-range proteinuria is above 3 to 3.5 g/day |
| 350 mg/dL | 3.50 g/day | Normal is typically under about 0.2 g/day; nephrotic-range proteinuria is above 3 to 3.5 g/day |
Questions
Why does the ratio approximate grams per day?
Because a typical adult excretes roughly 1 gram of creatinine daily. Dividing by creatinine effectively normalises to that daily output, so the ratio comes out in grams of protein per day without further arithmetic.
When does that assumption fail?
When creatinine excretion is unusual, which happens with very high or very low muscle mass, in extremes of body size and in rapidly changing kidney function. The estimate drifts accordingly.
Should the sample be a first morning one?
Usually, yes. A first morning specimen avoids the effect of upright posture, which increases protein excretion in some people and would otherwise inflate the result.
How does this compare to albumin-to-creatinine?
The albumin ratio is more sensitive and is preferred for early detection, particularly in diabetes. The protein ratio captures all urinary protein and is used when losses are larger.
For classifying acute kidney injury, see the FeNa calculator. For estimated filtration rate, see the creatinine clearance calculator.