Millimeter of Water Column to Atmosphere Converter

How do I convert mmH₂O to cmH₂O?

Simple: Divide by 10

1 cmH₂O = 10 mmH₂O

Examples (medical ventilators often use cmH₂O):

• 100 mmH₂O = 10 cmH₂O (PEEP setting)
• 200 mmH₂O = 20 cmH₂O (peak pressure)
• 50 mmH₂O = 5 cmH₂O (CPAP setting)
• 150 mmH₂O = 15 cmH₂O (typical ventilator)

Medical context: "PEEP of 5" means 5 cmH₂O = 50 mmH₂O

How do I convert mmH₂O to Pascals or mbar?

Formula:

• Pa = mmH₂O × 9.807
• mbar = mmH₂O × 0.09807

Examples:

• 100 mmH₂O = 981 Pa ≈ 9.8 mbar (CPAP)
• 200 mmH₂O = 1,961 Pa ≈ 19.6 mbar (ventilator)
• 50 mmH₂O = 490 Pa ≈ 4.9 mbar (low PEEP)
• 10 mmH₂O = 98 Pa ≈ 1 mbar (clean room)

Quick approximation: 100 mmH₂O ≈ 1 kPa

mmH₂O to Pascal converter →

What is normal CPAP pressure in mmH₂O?

Typical CPAP range: 40-140 mmH₂O (4-14 cmH₂O)

By severity:

• Mild sleep apnea: 40-60 mmH₂O (4-6 cmH₂O)
• Moderate sleep apnea: 60-100 mmH₂O (6-10 cmH₂O)
• Severe sleep apnea: 100-140 mmH₂O (10-14 cmH₂O)

Starting pressure: Usually 40 mmH₂O (4 cmH₂O), titrated upward

Maximum typical: 200 mmH₂O (20 cmH₂O) for severe cases

Note: CPAP machines usually display in cmH₂O, not mmH₂O

• Setting of "8" = 8 cmH₂O = 80 mmH₂O

What is PEEP in ventilators?

PEEP = Positive End-Expiratory Pressure

Pressure maintained in lungs at end of exhalation (prevents alveolar collapse)

Normal PEEP: 50 mmH₂O (5 cmH₂O) Moderate PEEP: 50-100 mmH₂O (5-10 cmH₂O) High PEEP: 100-200 mmH₂O (10-20 cmH₂O)

Used for:

• Oxygenation improvement
• Preventing lung collapse
• ARDS (Acute Respiratory Distress Syndrome)
• Pulmonary edema

Too high: Can cause lung damage (barotrauma) Too low: Alveoli collapse, poor oxygenation

Example ventilator settings:

• Peak pressure: 200 mmH₂O (20 cmH₂O)
• PEEP: 50 mmH₂O (5 cmH₂O)
• Tidal volume: 500 mL

Why use mmH₂O instead of kPa or mmHg?

Medical respiratory context:

mmH₂O preferred:

• Appropriate scale: Ventilator pressures 50-300 mmH₂O (vs 0.5-3 kPa - awkward decimals)
• Historical: Water manometers originally used
• Precision: 1 mmH₂O resolution appropriate for therapy adjustments
• International standard: ISO, medical device standards use cmH₂O/mmH₂O
• Clinical familiarity: Respiratory therapists trained in cmH₂O

Not mmHg because:

• mmHg too large (1 mmHg = 13.6 mmH₂O)
• mmHg used for blood pressure, not airway pressure
• Less precise for ventilator adjustments

Not kPa because:

• Requires decimal precision (8 cmH₂O = 0.78 kPa)
• Less intuitive for clinicians
• Though some modern ventilators offer kPa display option

Conversion: 100 mmH₂O = 10 cmH₂O = 0.98 kPa = 7.4 mmHg