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CPAP Pressure Calculator

Predict starting CPAP pressure based on BMI, AHI, neck circumference, and positional data using the Hoffstein prediction model.

About this calculator

This calculator implements the published Miljeteig and Hoffstein equation for predicting an obstructive sleep apnea (OSA) patient's effective CPAP pressure: P = 0.16 x BMI + 0.13 x Neck Circumference (cm) + 0.04 x AHI (events/hour) - 5.12, with a small +0.5 cmH2O male adjustment applied by this implementation on top of the published equation (male patients have historically been found to need modestly higher pressures on average, though this specific offset is this calculator's own simplification rather than a term in the original published formula). The result is clamped to the clinically typical CPAP range of 4-20 cmH2O, since prediction formulas can occasionally output values outside what a machine can deliver or a patient can tolerate. All three of BMI, Neck Circumference, and AHI raise the predicted pressure -- more body mass, a thicker neck, and more frequent apnea/hypopnea events each independently correlate with a higher effective therapeutic pressure in the published literature this formula was derived from.

The Titration Recommendation flags a patient for lab titration (rather than auto-CPAP) when overall AHI exceeds 30 (severe OSA) or when Supine AHI is more than double the overall AHI, since a strong positional component to the apnea can make auto-titrating devices less reliable. This formula predicts a median starting pressure for a population and is explicitly known in the literature to under- or over-estimate the correct pressure for individual atypical patients (e.g. lean patients, women, or very high-BMI patients) -- it is a starting point for clinical titration, not a substitute for it.

Inputs

in

Results

Predicted CPAP Pressure

7 cmH₂O

Pressure Range (low)5 cmH₂O
Pressure Range (high)9 cmH₂O
Titration RecommendationAuto-CPAP acceptable
OSA SeverityModerate
How to Use This Calculator
  1. Enter the patient's BMI in kg/m².
  2. Input the Apnea-Hypopnea Index (AHI) from the diagnostic polysomnography report.
  3. Enter neck circumference in cm and supine AHI if available.
  4. Review the estimated starting CPAP pressure range.
  5. Titrate final CPAP pressure through an attended titration study or auto-CPAP data.

How the result changes with BMI (kg/m²)

BMI (kg/m²)Predicted CPAP Pressure
164.4 cmH₂O
245.7 cmH₂O
489.5 cmH₂O
6011.4 cmH₂O

What each input means

BMI (kg/m²)
Body Mass Index. Higher BMI generally requires higher CPAP pressure.
AHI (events/hour)
Apnea-Hypopnea Index from sleep study. Mild: 5-15, Moderate: 15-30, Severe: 30+.
Neck Circumference
Measured at the level of the cricothyroid membrane.
Supine AHI (events/hour)
AHI when sleeping on the back. Higher than overall suggests positional apnea.
Gender
Male patients receive a +0.5 cmH₂O adjustment on top of the published formula (see FAQ).

What each result means

Titration Recommendation
Flags lab titration when overall AHI exceeds 30 or supine AHI is more than double overall AHI; otherwise auto-CPAP is acceptable.
OSA Severity
Normal: AHI < 5. Mild: 5-14. Moderate: 15-29. Severe: 30+.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    5 parameters
    BMI (kg/m²) = 32, AHI (events/hour) = 25, Neck Circumference (cm) = 42, Supine AHI (events/hour) = 35, Gender = 1 = 5 input(s) provided
  2. Calculate Predicted CPAP Pressure
    7 = 7
  3. Calculate Pressure Range (Low)
    5 = 5
  4. Calculate Pressure Range (High)
    Pressure Range (High)
    9 = 9

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

What formula does this calculator use to predict CPAP pressure?

It implements the published Miljeteig and Hoffstein prediction equation: P = 0.16 x BMI + 0.13 x Neck Circumference (cm) + 0.04 x AHI (events/hour) - 5.12. This is one of the earliest and most widely referenced formulas for estimating a starting therapeutic CPAP pressure from readily available anthropometric and sleep-study data, rather than requiring an in-lab titration study for every patient.

Why do all three main inputs raise the predicted pressure?

Each of BMI, Neck Circumference, and AHI carries a positive coefficient in the published equation because higher values of each have been independently associated with more severe upper-airway collapsibility requiring more pneumatic support to keep the airway open: a higher BMI and thicker neck both correlate with more soft-tissue crowding of the airway, while a higher AHI reflects more frequent airway collapse events during sleep.

Is the predicted pressure the final pressure a patient should use?

No. This is explicitly a starting-point prediction, clamped to the clinically typical 4-20 cmH2O range. The published literature behind this formula shows it predicts the median pressure well for typical patients but can meaningfully over- or under-estimate the correct pressure for atypical body types, so the actual therapeutic pressure should still be confirmed through an attended titration study or auto-CPAP titration data, as the howToUse guidance notes.

When does the calculator recommend a lab titration over auto-CPAP?

Titration Recommendation flags lab titration when overall AHI exceeds 30 (severe OSA) or when Supine AHI is more than double the overall AHI, which suggests a strong positional component to the sleep apnea. Auto-titrating devices can respond less predictably to apnea that is heavily position-dependent, so a supervised titration study is typically recommended in that situation.

Does patient gender affect the predicted pressure?

This implementation applies a small +0.5 cmH2O adjustment for male patients on top of the published Miljeteig-Hoffstein calculation, reflecting that male patients have broadly been observed to need somewhat higher pressures on average. That specific offset is a simplification added by this calculator, not a term present in the original published equation, so it should be read as a rough adjustment rather than a separately validated clinical factor.

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