AST/ALT Ratio Calculator
Calculate the ratio of AST to ALT from your laboratory results.
Your enzyme results
Before you calculate
ALT must be greater than zero.
A zero denominator cannot produce a valid ratio. Use the units shown on your report.
AST/ALT ratio
AST 45 ÷ ALT 30
Entered enzyme activities
How is this calculated?
Equipment guide
Read both values
Use AST and ALT from your laboratory report.
Match the units
Both enzyme activities must use matching units.
Use the same sample
Avoid combining different sampling dates.
Calculation & assumptions
AST/ALT ratio = AST ÷ ALT
The matching units cancel. This ratio is dimensionless. No age or sex inputs are required for the arithmetic.
Frequently asked questions
What is the AST/ALT ratio?
It is AST activity divided by ALT activity from matching laboratory results. AST stands for aspartate aminotransferase and ALT for alanine aminotransferase. This page performs the arithmetic and does not make a diagnosis.
Which values should I enter?
Enter AST and ALT activities in U/L from the same sample. Both must use matching units. Do not combine different sampling dates or enter a multiple of the upper reference limit as though it were an activity in U/L.
Why can't ALT be zero?
ALT is the denominator. Dividing by zero does not give a finite ratio, so the calculator clears the result and asks for a positive ALT value. Check your report if it lists zero or a result below a measurement limit.
Does the ratio have a unit?
No. The matching U/L units cancel when AST is divided by ALT, leaving a dimensionless ratio. This page accepts both activities in U/L.
Can this ratio diagnose a condition?
No. Liver blood tests require interpretation with your laboratory reference intervals, symptoms, medical history and other results. The ratio and comparison bars do not classify normality or diagnose liver disease or alcohol use.
More questions (5)
What does the AST/ALT Ratio calculate?
It divides the entered AST activity by the entered ALT activity. For AST 45 U/L and ALT 30 U/L, the ratio is exactly 1.50 to 1.
What formula does this calculator use?
AST/ALT ratio = AST (U/L) ÷ ALT (U/L). The worked reverse check uses ALT × (AST ÷ ALT), retaining the original division rather than multiplying by a rounded displayed ratio.
Why might my result differ from another source?
Check the units, sampling date and entered values. Display rounding and laboratory methods may differ. The bars show only the relative lengths of the entered activities, not reference limits or a clinical severity scale.
Does the result update automatically?
Yes. Editing either input updates the ratio, comparison and worked steps immediately. Invalid active inputs clear numerical results and disable copying and downloading.
What are the software input limits?
AST must be non-negative and ALT positive. Activities are limited to 1,000,000,000 U/L, with positive values at least 0.000000001 U/L and up to 12 decimal places. These are software bounds, not clinical reference ranges. A zero AST gives a mathematical ratio of zero and is not a clinical interpretation.
Sources & References
References provide context, not endorsement.
Page information
Updated: October 27, 2026