Amniotic Fluid Index (AFI) Calculator

Q: How is the amniotic fluid index (AFI) calculated?

The uterus is divided into four quadrants and the deepest vertical pocket of amniotic fluid (free of umbilical cord or fetal limbs) is measured in centimeters in each quadrant. The AFI is the sum of the four measurements.

Q: What is a normal AFI?

A normal AFI is generally cited as greater than 5.0 cm and less than 24.0 cm, with a median around 14 cm from about 20 to 35 weeks of gestation. Some sources use a 25.0 cm upper bound instead of 24.0 cm.

Q: What AFI indicates oligohydramnios?

An AFI of 5.0 cm or less is the classic cutoff for oligohydramnios. ACOG's current preferred diagnostic method is a single deepest vertical pocket (DVP) of 2 cm or less rather than AFI-based diagnosis.

Q: What AFI indicates polyhydramnios, and are there severity levels?

Polyhydramnios is generally diagnosed above the normal upper bound and is commonly graded by severity: mild 24.0-29.9 cm, moderate 30.0-34.9 cm, and severe 35.0 cm or higher.

Q: What is the difference between AFI and single deepest pocket (SDP/DVP)?

AFI sums the deepest vertical pocket from all four uterine quadrants. Single deepest pocket (SDP), also called deepest vertical pocket (DVP), uses only the single deepest pocket found anywhere in the uterus. ACOG now favors DVP for diagnosing oligohydramnios because AFI has been associated with more false-positive oligohydramnios diagnoses and higher rates of labor induction without improving outcomes.

Q: Does this calculator replace a clinician's assessment?

No. Amniotic fluid assessment supports but does not replace clinical judgment. Any diagnosis or management decision based on amniotic fluid volume must be made by the treating obstetric provider based on the full clinical picture.

AFI (cm)	Classification	Typical Significance
≤ 5.0	Oligohydramnios	Reduced fluid volume — correlate with gestational age, growth, and clinical picture.
> 5.0 – < 24.0	Normal	Typical fluid volume for gestational age; median ~14 cm from about 20–35 weeks.
24.0 – 29.9	Polyhydramnios (mild)	Frequently idiopathic; further evaluation may be considered depending on clinical context.
30.0 – 34.9	Polyhydramnios (moderate)	Higher likelihood of identifiable cause (e.g. maternal diabetes, fetal anomaly).
≥ 35.0	Polyhydramnios (severe)	Highest likelihood of underlying etiology; comprehensive fetal and maternal evaluation recommended.

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Walk-through

How to Use This Calculator

4 steps

1

Measure the deepest vertical pocket in each quadrant

On ultrasound, the uterus is divided into four quadrants using the linea nigra (vertical) and the umbilicus (horizontal) as dividers. In each quadrant, find the single deepest pocket of amniotic fluid that is free of umbilical cord and fetal limbs, and measure its vertical depth in centimeters.

2

Enter all four quadrant measurements

Enter the deepest vertical pocket for Quadrant 1 (right upper), Quadrant 2 (right lower), Quadrant 3 (left lower), and Quadrant 4 (left upper). All four are required — the AFI Total tab shows a prompt until every quadrant has a value.

3

Read the AFI total and classification

Once all four quadrants are entered, the AFI Total tab shows the sum in centimeters along with its classification: oligohydramnios, normal, or polyhydramnios (mild, moderate, or severe). The result updates instantly as you adjust any quadrant.

4

Check the Classification and Quadrant Breakdown tabs

Switch to Classification for the full band reference table with your current AFI highlighted, or Quadrant Breakdown for a per-quadrant summary suitable for documentation or export via the CSV button.

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Reference

Formula & Methodology

2 formulas

Amniotic Fluid Index (AFI)

AFI = Q1 + Q2 + Q3 + Q4

The AFI is the sum of the deepest vertical pocket of amniotic fluid (cm), free of umbilical cord or fetal limbs, measured in each of the four uterine quadrants (Phelan et al., 1987).

Classification bands

AFI ≤ 5.0 → Oligohydramnios; 5.0 < AFI < 24.0 → Normal; 24.0 ≤ AFI < 30.0 → Mild polyhydramnios; 30.0 ≤ AFI < 35.0 → Moderate polyhydramnios; AFI ≥ 35.0 → Severe polyhydramnios

Oligohydramnios and the normal range follow the classic AFI cutoffs (some sources use a 25.0 cm normal upper bound instead of 24.0 cm). Polyhydramnios severity tiers follow the mild/moderate/severe AFI cutoffs reported in AJOG's moderate-to-severe-polyhydramnios cutoff analysis.

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High YMYL

Trust, Methodology & Sources

Reviewed by Calculover Editorial Review · Updated 2026-07-23 · 2 sources

Editorial accountability

Author: Quinn Sumner - Editor

Owner: Quinn Sumner - Editorial owner

Reviewer: Calculover Editorial Review - Clinical-source review

Last reviewed: 2026-07-23

Last verified: 2026-07-23

Data effective: 2026-07-23

Methodology

The calculator implements the four-quadrant amniotic fluid index (AFI) technique exactly as published in Phelan JP, Ahn MO, Smith CV, Rutherford SE, Anderson E. "Amniotic fluid volume assessment with the four-quadrant technique at 36-42 weeks' gestation." J Reprod Med. 1987;32(7):540-542 — the uterus is divided into four quadrants and the deepest vertical pocket of fluid (cm), free of umbilical cord or fetal limbs, is summed across all four. Classification uses AFI <= 5.0 cm for oligohydramnios and AFI > 5.0 cm and < 24.0 cm for the normal range, consistent with standard clinical references and ACOG's antepartum fetal surveillance guidance; note that some sources cite the normal upper bound as 25.0 cm instead of 24.0 cm, a minor variance across the literature that this calculator does not silently resolve one way. Polyhydramnios severity tiers (mild 24.0-29.9 cm, moderate 30.0-34.9 cm, severe >= 35.0 cm) follow the AFI cutoffs reported in the AJOG moderate-to-severe-polyhydramnios cutoff analysis (Qureshey EJ et al., J Ultrasound Med, 2022 companion abstract).

Assumption: Each quadrant measurement is the deepest vertical pocket obtained by a qualified sonographer using the standard four-quadrant technique (linea nigra and umbilicus as dividers), free of umbilical cord and fetal limbs.

Assumption: The classic four-quadrant AFI method is used, not the single deepest pocket (SDP/DVP) alternative.

Assumption: Norms apply broadly across the roughly 20-42 week gestational-age range where AFI is clinically used; this calculator does not adjust classification by exact gestational age.

Limitations & guidance

ACOG's current preferred method for diagnosing oligohydramnios is a single deepest vertical pocket (DVP) of 2 cm or less, not AFI <= 5 cm — AFI-based diagnosis has been associated with more false-positive oligohydramnios calls and higher labor-induction rates without improved outcomes. This calculator implements AFI only, per its intended scope.

The normal AFI upper bound is cited as 24.0 cm here; some sources use 25.0 cm instead. The difference is minor but is not silently resolved — see the Classification tab's reference note.

AFI measurement is operator- and technique-dependent and can vary between sonographers and machines.

This is an educational and clinical-reference tool, not a substitute for the treating obstetric provider's complete assessment of gestational age, fetal growth, and maternal status.

Professional guidance: This calculator is for education and clinical reference only and is not medical advice, diagnosis, or treatment. Amniotic fluid assessment supports, but does not replace, the judgment of the treating obstetric provider evaluating the patient's full clinical picture. Any diagnosis or management decision related to oligohydramnios or polyhydramnios must be made by that provider.

Primary sources

Phelan JP, Ahn MO, Smith CV, Rutherford SE, Anderson E. Amniotic fluid volume assessment with the four-quadrant technique at 36-42 weeks' gestation. J Reprod Med. 1987;32(7):540-542

ACOG — Antepartum Fetal Surveillance (Practice Bulletin), including amniotic fluid volume assessment guidance

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Glossary

Key Terms Explained

6 terms

Amniotic fluid index (AFI) A semi-quantitative estimate of amniotic fluid volume, computed by summing the deepest vertical pocket of fluid measured by ultrasound in each of the four uterine quadrants. Introduced by Phelan et al. in 1987.

Deepest vertical pocket (DVP) Also called single deepest pocket (SDP). The depth, in centimeters, of the single largest pocket of amniotic fluid found anywhere in the uterus (or within one quadrant, for the AFI technique), free of umbilical cord and fetal limbs.

Oligohydramnios Reduced amniotic fluid volume, classically defined as an AFI of 5.0 cm or less. ACOG's currently preferred diagnostic method uses a deepest vertical pocket of 2 cm or less instead of AFI.

Polyhydramnios Excess amniotic fluid volume, generally diagnosed above the normal AFI upper bound (commonly cited as 24.0 or 25.0 cm) and graded by severity: mild, moderate, or severe.

Four-quadrant technique The AFI measurement method in which the uterus is divided into four quadrants by the linea nigra and the umbilicus, and the deepest vertical pocket in each quadrant is measured and summed.

Single deepest pocket (SDP) An alternative amniotic fluid assessment method that uses only the single deepest pocket found anywhere in the uterus, rather than summing four quadrant measurements. ACOG now favors SDP/DVP over AFI for diagnosing oligohydramnios because AFI has been associated with more false-positive oligohydramnios diagnoses and higher labor-induction rates without a corresponding improvement in outcomes.

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Scenarios

Real-World Examples

3 worked examples

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Reduced fluid volume at a growth ultrasound

Oligohydramnios — AFI 4.0 cm

Quadrant 1 1.0 cm Quadrant 2 1.5 cm Quadrant 3 1.0 cm Quadrant 4 0.5 cm

The four quadrants sum to 1.0 + 1.5 + 1.0 + 0.5 = 4.0 cm. An AFI of 4.0 cm is at or below the 5.0 cm oligohydramnios cutoff, indicating reduced amniotic fluid volume that warrants correlation with gestational age, fetal growth, and the broader clinical picture.

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Routine third-trimester fluid check

Normal — AFI 14.0 cm

Quadrant 1 3.0 cm Quadrant 2 4.0 cm Quadrant 3 3.0 cm Quadrant 4 4.0 cm

The four quadrants sum to 3.0 + 4.0 + 3.0 + 4.0 = 14.0 cm, close to the median AFI for weeks 20-35 of gestation and comfortably within the normal range (greater than 5.0 cm, less than 24.0 cm).

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Excess fluid flagged on anatomy scan

Severe polyhydramnios — AFI 37.0 cm

Quadrant 1 9.0 cm Quadrant 2 10.0 cm Quadrant 3 9.0 cm Quadrant 4 9.0 cm

The four quadrants sum to 9.0 + 10.0 + 9.0 + 9.0 = 37.0 cm, at or above the 35.0 cm severe-polyhydramnios threshold. Severe polyhydramnios carries the highest likelihood of an identifiable underlying cause and typically prompts further maternal and fetal evaluation.

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Deep Dive

Understanding the Amniotic Fluid Index Calculator

3 chapters · 5 min read

The amniotic fluid index (AFI) is one of the two standard ultrasound methods for estimating how much amniotic fluid surrounds the fetus, alongside the single deepest pocket (SDP/DVP) technique. Introduced by Phelan and colleagues in 1987, it sums four quadrant measurements into a single number used to screen for oligohydramnios (too little fluid) and polyhydramnios (too much). This article explains how the AFI is measured, how to read the classification, and where the method's limits lie.

How the AFI is measured

The uterus is divided into four quadrants using the linea nigra as the vertical divider and the umbilicus as the horizontal divider. In each quadrant, the sonographer finds the single deepest pocket of amniotic fluid — free of umbilical cord loops and fetal limbs — and measures its vertical depth in centimeters, with the transducer held perpendicular to the floor.

The AFI is simply the sum of the four measurements. Because it is a sum rather than a single deepest-pocket reading, the AFI tends to run higher than the single deepest pocket (SDP) method for the same true fluid volume, which is part of why the two methods use different cutoffs.

Reading oligohydramnios vs. polyhydramnios

The classic AFI cutoffs place oligohydramnios at 5.0 cm or below, normal fluid from just above 5.0 cm up to just under 24.0 cm (median about 14 cm from roughly 20 to 35 weeks), and polyhydramnios above that. Some references cite the normal upper bound as 25.0 cm instead of 24.0 cm — the difference between sources is minor and both are in common clinical use.

Polyhydramnios is commonly graded by severity — mild (24.0-29.9 cm), moderate (30.0-34.9 cm), and severe (35.0 cm or higher) — because the likelihood of finding an identifiable cause (such as maternal diabetes, fetal anomaly, or infection) and the risk of adverse outcomes both rise with severity.

Limits — AFI vs. DVP, and why single deepest pocket is increasingly preferred

The American College of Obstetricians and Gynecologists (ACOG) now recommends the single deepest pocket (SDP), also called deepest vertical pocket (DVP), of 2 cm or less to diagnose oligohydramnios, rather than an AFI of 5 cm or less. Randomized trial evidence found that using AFI led to more oligohydramnios diagnoses and more labor inductions than SDP, without improving perinatal outcomes — meaning AFI tends to over-diagnose low fluid relative to SDP.

This calculator implements the classic four-quadrant AFI method only, as specified. It is an estimate, not a direct fluid-volume measurement, and is operator- and technique-dependent. It is for education and clinical reference only — amniotic fluid assessment and any resulting management decision must be made by the treating obstetric provider based on the complete clinical picture, including gestational age, fetal growth, and maternal status.

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Questions

Frequently Asked Questions

8 questions

How is the amniotic fluid index (AFI) calculated?+

The uterus is divided into four quadrants and the deepest vertical pocket of amniotic fluid — free of umbilical cord or fetal limbs — is measured in centimeters in each quadrant. The AFI is the sum of the four measurements.

What is a normal AFI?+

A normal AFI is generally cited as greater than 5.0 cm and less than 24.0 cm, with a median around 14 cm from about 20 to 35 weeks of gestation. Some sources use a 25.0 cm upper bound instead of 24.0 cm; both are in common clinical use.

What AFI indicates oligohydramnios?+

An AFI of 5.0 cm or less is the classic cutoff for oligohydramnios. ACOG's current preferred diagnostic method is a single deepest vertical pocket (DVP) of 2 cm or less rather than AFI-based diagnosis, since AFI has been associated with more false-positive oligohydramnios diagnoses.

What AFI indicates polyhydramnios, and are there severity levels?+

Polyhydramnios is generally diagnosed above the normal upper bound and is commonly graded by severity: mild 24.0-29.9 cm, moderate 30.0-34.9 cm, and severe 35.0 cm or higher. Severity correlates with a higher likelihood of an identifiable underlying cause.

What is the difference between AFI and single deepest pocket (SDP/DVP)?+

AFI sums the deepest vertical pocket from all four uterine quadrants. Single deepest pocket (SDP), also called deepest vertical pocket (DVP), uses only the single deepest pocket found anywhere in the uterus. ACOG now favors DVP for diagnosing oligohydramnios because AFI has been associated with more false-positive oligohydramnios diagnoses and higher rates of labor induction without improving outcomes.

Why does the calculator ask for all four quadrants before showing a result?+

The AFI is only meaningful as the sum of all four quadrant measurements — a partial sum would misrepresent the total fluid volume. The calculator shows a prompt for any quadrant still missing and only computes the AFI once all four are entered.

Can I share my results?+

Yes. The calculator encodes your four quadrant values into the URL, so copying the link after entering your measurements is enough to share the exact scenario with a colleague.

Does this calculator replace a clinician's assessment?+

No. Amniotic fluid assessment supports but does not replace clinical judgment. Any diagnosis or management decision based on amniotic fluid volume must be made by the treating obstetric provider based on the full clinical picture.

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Deepest Vertical Pocket, per Uterine Quadrant