A Creatinine clearance calculator estimates creatinine clearance (CrCl) using the Cockcroft–Gault equation from age, body weight, sex, and serum creatinine.

The result is expressed in:

mL/min

Cockcroft–Gault estimates are still encountered in medication references and prescribing information, but they should not automatically be substituted for every laboratory-reported eGFR value. Drug labels and clinical protocols may specify different renal-function measures or calculation methods. NIDDK notes that FDA-approved drug labeling has used several approaches over time, including measured CrCl, Cockcroft–Gault eCrCl, MDRD, and CKD-EPI estimates.

Clinical warning: Do not diagnose kidney disease, start or stop medication, or change a dose from this calculator alone. Confirm the required kidney-function measure, creatinine units, body-weight convention, current prescribing information, and individual clinical circumstances with a qualified clinician or pharmacist.

Check the units and the weight value before calculating. A mathematically correct Cockcroft–Gault result can still be inappropriate for a clinical decision if the wrong inputs or renal-function measure are used.

What the calculator needs

The traditional Cockcroft–Gault calculation uses:

Age in years

Body weight in kilograms

Serum creatinine in mg/dL

and:

Sex

These values are combined to estimate creatinine clearance.

The calculator does not directly measure filtration or urine creatinine clearance.

The Cockcroft–Gault equation

The traditional equation for males is:

CrCl = ((140 − Age) × Weight in kg) ÷ (72 × Serum creatinine in mg/dL)

The historical female adjustment multiplies the result by:

0.85

So the traditional female form can be written:

CrCl = [((140 − Age) × Weight) ÷ (72 × Serum creatinine)] × 0.85

The result is expressed in:

mL/min

These equations should be understood as historical estimating equations rather than direct measurements of renal clearance.

How to use the Creatinine clearance calculator

1. Enter age in years.
2. Select the appropriate sex input used by the calculator.
3. Enter the body weight required by the relevant protocol.
4. Confirm whether weight is entered in kilograms or pounds.
5. Enter the serum creatinine value.
6. Confirm whether creatinine is in mg/dL or µmol/L.
7. Calculate the estimated CrCl.
8. Review the exact inputs used.
9. Before applying the result to medication dosing, confirm that the drug reference actually calls for Cockcroft–Gault CrCl and the same weight convention.

The final step is especially important because different medication references may specify different kidney-function metrics.

Convert pounds to kilograms correctly

If body weight is supplied in pounds:

Weight in kg = Weight in lb ÷ 2.20462

For example:

176 lb ÷ 2.20462 ≈ 79.8 kg

Using:

176

as though it were kilograms would produce a substantially different estimate.

Always match the number to the selected unit.

Check serum creatinine units before calculating

Serum creatinine may be reported as:

mg/dL

or:

µmol/L

The traditional Cockcroft–Gault formula above expects:

mg/dL

A commonly used creatinine-specific conversion is approximately:

Serum creatinine in mg/dL = Serum creatinine in µmol/L ÷ 88.4

For example:

88.4 µmol/L ≈ 1.0 mg/dL

and:

176.8 µmol/L ≈ 2.0 mg/dL

A unit error here can dramatically change the calculated CrCl.

If the calculator provides automatic unit conversion, make sure the selected unit matches the laboratory report exactly.

Worked example

Suppose a:

60-year-old man

weighs:

80 kg

and has serum creatinine:

1.0 mg/dL

Use:

CrCl = ((140 − 60) × 80) ÷ (72 × 1.0)

First:

140 − 60 = 80

Then:

80 × 80 = 6,400

Denominator:

72 × 1.0 = 72

So:

6,400 ÷ 72 ≈ 88.9

Estimated creatinine clearance:

≈ 88.9 mL/min

Input	Example value
Age	60 years
Weight	80 kg
Serum creatinine	1.0 mg/dL
Equation	Traditional Cockcroft–Gault
Estimated CrCl	≈ 88.9 mL/min

This example demonstrates the arithmetic only.

It does not identify a diagnosis, kidney-disease stage, or medication dose.

What happens when the historical female factor is applied

Using the same numerical inputs but applying the traditional:

0.85

female adjustment:

88.9 × 0.85 ≈ 75.6 mL/min

That difference illustrates why the sex input is part of the traditional equation.

It should not be interpreted as a direct biological measurement of kidney function.

CrCl is an estimate

Cockcroft–Gault does not directly measure how much creatinine is cleared from the body.

It estimates clearance from:

• age;
• weight;
• serum creatinine;
• and the equation’s sex coefficient.

A measured creatinine clearance is a separate test that can involve urine collection and blood testing.

The two should not be assumed to be identical.

CrCl and eGFR are not interchangeable numbers

A laboratory may report:

eGFR in mL/min/1.73 m²

while Cockcroft–Gault produces:

estimated CrCl in mL/min

These quantities are related to kidney function but come from different equations and may use different normalization.

Current NIDDK adult eGFR resources use race-free CKD-EPI equations, including the 2021 creatinine and creatinine-cystatin C equations.

Do not replace one value with the other merely because both appear to describe kidney function.

Why 1.73 m² appears on laboratory eGFR

Many commonly reported eGFR values are normalized to a standard body surface area of:

1.73 m²

That allows kidney function to be compared across body sizes for purposes such as CKD assessment.

Cockcroft–Gault CrCl is traditionally reported as:

mL/min

without that same normalized unit.

This is one reason the numerical values may differ even when they are calculated from the same serum creatinine result.

Drug dosing may specify a particular renal metric

The correct renal-function input for a medication should come from the current prescribing information or relevant clinical protocol.

NIDDK notes that FDA does not favor one single estimating equation for every drug-dosing situation and that FDA-approved labels have historically used several kidney-function approaches.

Therefore:

“My laboratory eGFR is X”

and:

“My Cockcroft–Gault CrCl is Y”

should not automatically lead to the assumption that either number can replace the other for every medication.

Do not convert a laboratory eGFR casually

A BSA-normalized eGFR can sometimes be expressed in nonindexed:

mL/min

using body surface area when a specific purpose calls for it.

But that conversion is not the same thing as calculating Cockcroft–Gault CrCl.

NIDDK discusses removal of BSA indexing for some drug-dosing situations, particularly when body size differs substantially from average, but the appropriate method depends on the clinical use.

Do not perform such conversions for a medication decision unless the relevant validated method calls for them.

Which body weight should be entered?

This is one of the most important practical limitations of a Cockcroft–Gault calculator.

Different protocols may use:

• actual body weight;
• ideal body weight;
• adjusted body weight;
• or another specified approach

depending on patient characteristics and the clinical application.

There is no single weight substitution rule that should automatically be applied to every person and every medication.

Use the body-weight method specified by the relevant drug reference, institutional protocol, or clinician.

Record which weight was used

Suppose two calculations use the same:

age

sex

and:

serum creatinine

but one uses:

70 kg

and another uses:

90 kg

Because weight appears directly in the numerator, the CrCl results will differ substantially.

A useful clinical calculation record should therefore include:

Weight = 80 kg, actual body weight

or:

Weight = [value], adjusted according to [relevant protocol]

rather than recording only the final CrCl.

Two calculators can disagree without either using different algebra

If two websites return different CrCl values, possible reasons include:

• different weight conventions;
• different unit conversions;
• different rounding;
• different handling of sex;
• different treatment of extreme inputs;
• or data-entry differences.

Compare the inputs before assuming the formula itself differs.

Serum creatinine is influenced by more than kidney filtration

Serum creatinine is related to kidney function, but it is also influenced by creatinine production and other factors.

NIDDK notes that creatinine-based estimating equations can be affected by factors such as body size, muscle mass, diet, and tubular secretion. It recommends considering alternative or confirmatory approaches in situations where creatinine-based estimates may be inaccurate, particularly when clinical decisions are sensitive to the result.

This is why a mathematically precise calculator output should not be mistaken for a perfectly precise measurement of kidney function.

Low muscle mass can affect interpretation

A person with unusually low muscle mass may generate less creatinine.

Examples can include some people with:

• frailty;
• significant muscle wasting;
• amputation;
• prolonged illness;
• or other causes of reduced muscle mass.

A serum-creatinine-based equation may therefore be less representative of actual filtration in some of these situations.

Clinical interpretation matters more than adding additional decimal places to the calculated result.

Unusually high muscularity can also matter

Someone with substantially greater muscle mass may produce more creatinine than an average person of similar age.

This can affect serum creatinine independently of kidney filtration.

Again, the calculator does not measure body composition and cannot automatically correct for an unusual relationship between muscle mass and creatinine production.

Rapidly changing kidney function is a major limitation

Creatinine-based equations generally assume a relatively stable relationship between serum creatinine and kidney function.

During rapidly changing kidney function, serum creatinine may not yet reflect the new steady state.

Examples can include acute illness or acute changes in renal function.

In these circumstances, a single calculated CrCl may not represent current clearance adequately.

A clinician may use trends, repeat measurements, other biomarkers, measured clearance, or another assessment depending on the situation.

One old laboratory result may not represent today

A creatinine value from months ago can be mathematically entered into the equation.

That does not mean it still represents current renal function.

Changes in:

• illness;
• hydration;
• medications;
• kidney function;
• body weight;
• or health status

can make an older value unsuitable for a current clinical decision.

Use a value appropriate to the purpose and timing of the decision.

Creatinine assay history matters to the equation

Cockcroft–Gault was developed decades ago, before modern standardized creatinine assays and newer GFR estimating equations.

That history helps explain why values from Cockcroft–Gault, modern eGFR equations, and measured kidney function do not always align perfectly.

Current NIDDK guidance emphasizes newer CKD-EPI equations for eGFR assessment while also recognizing that drug labels have been developed using multiple renal-function metrics over time.

Cystatin C can provide additional information

Modern kidney-function assessment can also use:

cystatin C

either alone or combined with creatinine.

NIDDK states that the combined 2021 CKD-EPI creatinine-cystatin C equation provides greater accuracy and lower bias than creatinine-only estimation in many circumstances and can be particularly useful when eGFR is near a critical decision threshold.

That does not mean cystatin C should simply be substituted into Cockcroft–Gault.

It belongs to different estimating methods.

Medication thresholds deserve extra care

Suppose a drug reference changes dosing recommendations around a specific kidney-function cutoff.

If a calculated result lies very close to that cutoff, small differences from:

• creatinine measurement;
• equation choice;
• body weight;
• rounding;
• or biological variability

may affect classification.

This is precisely the kind of situation where the final decision should not come from a generic calculator alone.

Check the current drug labeling and clinical interpretation.

Do not round inputs too early

Suppose body weight is:

79.6 kg

and serum creatinine is:

1.14 mg/dL

Rounding immediately to:

80 kg

and:

1.1 mg/dL

changes both numerator and denominator.

For an educational calculation this may be acceptable if stated.

For a clinical calculation, retain appropriate input precision and round the final displayed estimate according to the method being used.

More decimal places do not mean more clinical accuracy

A calculator might display:

63.47291 mL/min

That does not imply kidney clearance is known to five decimal places.

The formula itself is an estimate based on measured and demographic inputs.

Reporting something like:

63.5 mL/min

may be easier to read, but the appropriate precision depends on the clinical context.

Avoid confusing numerical display precision with biological certainty.

Check the calculation independently

Suppose the result is:

88.9 mL/min

for:

Age = 60

Weight = 80 kg

SCr = 1.0 mg/dL

Recalculate:

140 − 60 = 80

80 × 80 = 6,400

72 × 1.0 = 72

6,400 ÷ 72 ≈ 88.9

This verifies the arithmetic.

It does not validate whether:

• 80 kg was the correct weight convention;
• the creatinine was current;
• or CrCl was the correct metric for the clinical decision.

A useful input audit

Before using a Cockcroft–Gault result, verify:

Check	Question
Age	Is the current age entered correctly?
Weight	Is this the weight convention required by the protocol?
Weight unit	Is the value actually in kg?
Creatinine	Is the laboratory value recent and appropriate?
Creatinine unit	Is it mg/dL or µmol/L?
Stability	Is kidney function reasonably stable?
Equation	Does the clinical source call for Cockcroft–Gault?
Output	Is the result being interpreted as mL/min rather than automatically as normalized eGFR?

This review is often more important than recalculating the same equation several times.

Common creatinine-clearance calculation mistakes to avoid

Using pounds directly

Convert to kilograms unless the calculator performs the conversion automatically.

Entering µmol/L as though it were mg/dL

Confirm the laboratory unit first.

Assuming laboratory eGFR and Cockcroft–Gault CrCl are identical

They are different estimates.

Choosing a body-weight method without checking the protocol

Actual, ideal, or adjusted weight may produce different results.

Using an old creatinine result automatically

The value may no longer represent current kidney function.

Ignoring unstable kidney function

Steady-state estimating equations can become less reliable when renal function is changing rapidly.

Treating a calculator output as a diagnosis

CrCl alone does not diagnose kidney disease.

Changing medication from the number alone

The relevant drug label, clinical context, and prescribing guidance still control the decision.

Related calculations

Use the Dose Calculator only when the actual dose instruction has already been independently verified.

A Dose Calculator can perform arithmetic such as:

prescribed amount × body weight

or:

dose required ÷ concentration

but it should not generate a renal dose from a CrCl result unless a qualified source has already established the dosing rule.

The Body Surface Area Calculator can illustrate BSA calculations and help explain why some kidney-function values are indexed to:

1.73 m²

However, do not use BSA to convert clinical kidney-function values unless the relevant validated method specifically requires that conversion.

FAQ

What does CrCl mean?

CrCl means:

creatinine clearance

The Cockcroft–Gault equation provides an estimated CrCl based on age, body weight, sex, and serum creatinine.

What units does Cockcroft–Gault CrCl use?

The traditional result is expressed in:

mL/min

Is CrCl the same as eGFR?

No.

They are related kidney-function estimates but use different equations and can use different units or body-size normalization.

Why does my laboratory report mL/min/1.73 m²?

Many modern eGFR equations report GFR normalized to a standard body surface area of:

1.73 m²

Cockcroft–Gault CrCl is traditionally reported as:

mL/min

Which kidney-function number should be used for medication dosing?

Use the measure specified by the current drug labeling, validated clinical protocol, or treating clinician or pharmacist.

There is no single rule that every medication uses the same kidney-function equation.

Which body weight should I use?

That depends on the clinical protocol and patient context.

Different approaches may specify actual, ideal, or adjusted body weight.

Do not assume one weight method applies to every drug or patient.

What if my weight is in pounds?

Convert:

kg = lb ÷ 2.20462

unless the calculator performs the conversion automatically.

How do I convert serum creatinine from µmol/L?

A commonly used creatinine conversion is approximately:

mg/dL = µmol/L ÷ 88.4

Check that the laboratory value and calculator unit match.

Can I use a creatinine result from several months ago?

A clinician or pharmacist should determine whether an older laboratory value is suitable for the current decision.

Kidney function can change over time.

Why can low muscle mass affect the estimate?

Creatinine production is related partly to muscle mass.

A creatinine-based equation may therefore be less representative in people with unusually low or high muscle mass.

Can the calculator be used during acute kidney injury?

A steady-state creatinine equation may be unreliable when kidney function is changing rapidly.

Clinical assessment and repeat or alternative measurements may be required.

Is measured creatinine clearance the same as Cockcroft–Gault?

No.

Cockcroft–Gault provides an estimate.

Measured creatinine clearance is obtained through a separate measurement process.

Does a low CrCl diagnose chronic kidney disease?

Not by itself.

Diagnosis and staging require appropriate clinical evaluation and the kidney-function measures relevant to that purpose.

Can I use the result to change a medication dose?

Not from the calculator alone.

Confirm the current drug labeling, renal-function metric, patient-specific factors, and prescribing guidance with a clinician or pharmacist.

Why do two CrCl calculators give different answers?

Check:

• weight convention;
• units;
• sex adjustment;
• rounding;
• age;
• and serum creatinine.

Those differences can change the result even when both calculators are based on Cockcroft–Gault.

Kidney-function and drug-dosing references

NIDDK provides current professional guidance on kidney-function estimation for drug dosing and explains why different equations and body-surface-area conventions may be used in different situations.

NIDDK’s current adult eGFR resources describe the race-free 2021 CKD-EPI equations and the role of combined creatinine-cystatin C estimation.

The FDA’s current guidance on renal impairment and pharmacokinetics discusses assessment of renal function in drug development and dosing information.

Treat the equation and the clinical decision as separate steps

A Creatinine clearance calculator can perform Cockcroft–Gault arithmetic consistently.

That is the straightforward part.

The harder question is whether the resulting number is the correct kidney-function estimate for the decision being made.

Before using a CrCl result clinically, confirm:

the creatinine unit

the body-weight convention

the stability and timing of the laboratory value

the equation required by the relevant source

and:

the current medication labeling or clinical protocol

The calculator can estimate CrCl. It cannot determine diagnosis, medication safety, or the appropriate treatment plan for an individual patient.