Amniotic Fluid Index Calculator
The Amniotic Fluid Index (AFI) estimates the volume of amniotic fluid around the baby. The uterus is divided into four quadrants and the deepest vertical fluid pocket in each is measured by ultrasound. The four measurements are added together to give the AFI in centimetres. This calculator sums your four quadrant values and flags the result against common reference ranges. It is for information only and does not replace clinical assessment.
AFI formula
AFI = Q1 + Q2 + Q3 + Q4
each Q = deepest vertical fluid pocket in that quadrant (cm)
Common reference: 8 to 18 cm is normal
The AFI is simply the sum of the four quadrant pocket depths. Widely used reference ranges classify under 5 cm as oligohydramnios (low fluid) and over about 24 to 25 cm as polyhydramnios (high fluid), with normal in between.
Worked example
Quadrant pockets of 4, 3.5, 4 and 3 cm: AFI = 4 + 3.5 + 4 + 3 = 14.50 cm, which falls within the commonly cited normal range of 8 to 18 cm.
Frequently asked questions
What is a normal amniotic fluid index?
A frequently cited normal AFI is about 8 to 18 cm, though references vary and AFI changes with gestational age. An AFI below 5 cm suggests low fluid (oligohydramnios) and above roughly 24 to 25 cm suggests high fluid (polyhydramnios). Your clinician interprets the value in context.
How is each pocket measured?
The uterus is divided into four quadrants by the midline and a transverse line. In each quadrant the sonographer measures the deepest vertical pocket of fluid free of fetal parts and cord, in centimetres. The four depths are summed.
Does AFI replace clinical judgement?
No. AFI is one tool among several, including single deepest pocket measurement. This calculator only sums your entered values for information. Any abnormal result must be assessed by your maternity care team.
Sources
- U.S. National Library of Medicine (MedlinePlus): amniotic fluid and ultrasound.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.