CPAP Pressure Calculator - Hoffstein Formula

VivaRespire is a specialist online CPAP shop. We do not offer INAMI/RIZIV reimbursement. For more information, see our page on CPAP reimbursement in Belgium.

Important: this calculator is an educational tool. It does not constitute a medical prescription and does not replace titration or the advice of a sleep specialist.

CPAP pressure refers to the level of air pressure required to keep the upper airways open during sleep. It depends on several individual factors and cannot be the same for every patient.

This page provides an educational CPAP pressure calculator, based on the Hoffstein formula, which has been used in clinical research to estimate a theoretical therapeutic pressure from simple parameters: BMI, neck circumference and apnea-hypopnea index (AHI).

What is CPAP pressure?

CPAP pressure is the air pressure (expressed in cmH₂O) required to keep the upper airways open during sleep.

Its purpose is to:

prevent apneas and hypopneas,
stabilize breathing,
improve oxygenation and sleep quality.

This pressure is sometimes referred to as therapeutic pressure, target pressure or optimal pressure. To understand how your AHI influences the recommended pressure, see our page on the AHI - apnea-hypopnea index.

Why is CPAP pressure different for each patient?

There is no "standard" CPAP pressure that works for everyone. The required pressure depends on:

body morphology (weight, neck size),
severity of sleep apnea,
sleep position (back / side),
REM sleep,
nasal congestion,
mask leaks.

This is why some patients look for an estimated CPAP pressure for educational purposes, before or after medical follow-up.

Parameters used in the calculation

BMI (Body Mass Index)

BMI reflects the anatomical load on the upper airways. A higher BMI is statistically associated with a higher pressure requirement.

Neck circumference

Neck circumference is an indirect indicator of upper airway size and is commonly used when assessing sleep apnea risk.

AHI (Apnea-Hypopnea Index)

AHI corresponds to the number of respiratory events per hour of sleep, measured during a sleep study. Higher AHI values are generally associated with higher therapeutic pressure needs. Learn more about the AHI and how to interpret your results.

The formula used (Hoffstein)

The calculator below uses a formula published in clinical research to estimate a theoretical CPAP therapeutic pressure based on BMI, neck circumference and AHI.

Formula (estimation):

Pressure (cmH₂O) = 0.16 × BMI + 0.13 × Neck circumference (cm) + 0.04 × AHI − 5.12

This formula provides an indicative value (order of magnitude only). It does not replace titration or medical advice.

Calculate my theoretical CPAP pressure

The result represents an educational estimate based on the Hoffstein formula. It helps understand the approximate pressure range and facilitates discussion with a sleep specialist or sleep clinic.

For an additional interactive tool: Interactive calculator - Association Apnée →

How should the result be interpreted?

Fixed CPAP

A fixed CPAP delivers a single pressure throughout the night. The estimated value corresponds to a theoretical therapeutic target pressure.

APAP (automatic CPAP)

An APAP automatically adjusts pressure within a minimum and maximum range. The calculator may display a central theoretical value with an indicative range (± 2 cmH₂O).

This range is not a setting recommendation, but an illustration of how automatic devices operate.

Ramp pressure vs therapeutic pressure

Ramp pressure: low pressure at sleep onset, intended for comfort.
Therapeutic pressure: effective pressure required to prevent apneas.

The calculator refers only to therapeutic pressure, not ramp settings.

What to do once you have an estimated pressure?

Estimated pressure is a starting point. Effective treatment depends on accurate device settings, the right mask, and regular monitoring of your nightly data. Our guide on well-adjusted CPAP pressure walks you through the next steps.

When should you consult or reassess?

Even with appropriate pressure, certain symptoms should prompt medical review:

persistent daytime sleepiness despite treatment,
frequent or non-restorative awakenings,
snoring while using CPAP,
significant mask leaks,
recent weight gain,
dryness, discomfort or poor adherence.

In such cases, a medical reassessment is recommended.

Summary table: common CPAP pressure ranges

Pressure range	Typical clinical meaning
4 - 8 cmH₂O	Low pressure - mild to moderate apneas, less pronounced morphology
8 - 12 cmH₂O	Intermediate range - most common cases
12 - 16 cmH₂O	High pressure - severe apneas or high BMI
> 16 cmH₂O	Very high pressure - specific cases, close medical supervision

These ranges are indicative. Only your doctor or sleep specialist can determine the appropriate pressure for your situation.

Conclusion

This CPAP pressure calculator aims to help understand the factors influencing therapeutic pressure and better interpret information related to sleep apnea treatment.

Treatment comfort and effectiveness depend not only on pressure, but also on the equipment used and regular follow-up. To go further, see our guide on well-adjusted CPAP pressure.