Understanding Pressure Conversions

Pressure conversion is essential for tire maintenance, weather forecasting, scuba diving, industrial applications, and scientific work. Different regions and industries use various pressure units, making accurate conversion crucial for safety and proper equipment operation.

Common Pressure Units

Unit	Common Uses	Typical Range
PSI (lb/in²)	US tire pressure, industrial	Car tires: 30-35 PSI
Bar	European tire pressure, diving	Car tires: 2.0-2.5 bar
Pascal (Pa)	SI unit, scientific standard	Very small, usually use kPa
Atmosphere (atm)	Diving, scientific reference	Sea level: 1 atm
Kilopascal (kPa)	Canadian tire pressure, weather	Car tires: 200-250 kPa
mmHg / Torr	Blood pressure, vacuum systems	Blood pressure: 120/80 mmHg

Quick Conversion Reference

From	To	Multiply By	Example
PSI	Bar	0.0689476	30 PSI = 2.07 bar
Bar	PSI	14.5038	2 bar = 29 PSI
PSI	kPa	6.89476	30 PSI = 207 kPa
Bar	kPa	100	2 bar = 200 kPa
atm	PSI	14.6959	1 atm = 14.7 PSI
atm	Bar	1.01325	1 atm = 1.013 bar

Practical Applications

Tire Pressure

Proper tire inflation is critical for safety, fuel efficiency, and tire longevity. US tires show PSI, European tires show bar, Canadian tires show kPa. Most passenger cars require 30-35 PSI (2.0-2.4 bar or 200-240 kPa). Check your vehicle's door jamb sticker for exact specifications.

Weather and Atmospheric Pressure

Barometric pressure affects weather patterns. Standard atmospheric pressure at sea level is 1 atm = 14.7 PSI = 1.013 bar = 101.325 kPa = 760 mmHg. High pressure (above 1020 mb) indicates fair weather, low pressure (below 980 mb) suggests storms.

Scuba Diving

Divers measure tank pressure in PSI or bar. A full scuba tank contains about 3000 PSI (207 bar). Water pressure increases by 1 atm every 10 meters (33 feet) of depth. At 20 meters deep, a diver experiences 3 atm total pressure.

Medical Applications

Blood pressure is measured in mmHg (millimeters of mercury). Normal blood pressure is 120/80 mmHg, where 120 is systolic (heart contracting) and 80 is diastolic (heart relaxing). This equals 2.32/1.55 PSI or 0.16/0.11 bar.

Industrial and Engineering

Hydraulic systems, compressed air tools, and pressure vessels use PSI or bar depending on region. Safety specifications must be followed precisely - overpressure can cause equipment failure or explosions.

Common Pressure Reference Points

Description	PSI	Bar	kPa
Sea level atmospheric	14.7	1.013	101.3
Car tire (typical)	32	2.2	220
Bike tire (road)	80-130	5.5-9.0	550-900
Soccer ball	8-16	0.6-1.1	60-110
Pressure cooker	15	1.0	100
Scuba tank (full)	3000	207	20,700

Absolute vs Gauge Pressure

Understanding the difference is important:

• Absolute pressure: Measured relative to perfect vacuum (0 pressure)
• Gauge pressure: Measured relative to atmospheric pressure
• Example: 30 PSI gauge = 44.7 PSI absolute (30 + 14.7)
• Most tire gauges: Show gauge pressure, not absolute
• Notation: PSIA (absolute), PSIG (gauge)

Tips for Pressure Measurement

• Check tires cold: Driving heats tires, increasing pressure by 4-6 PSI
• Use proper gauge: Digital gauges are more accurate than analog stick gauges
• Seasonal adjustment: Tire pressure drops ~1 PSI per 10°F temperature decrease
• Don't overinflate: Reduces traction and causes uneven wear
• Check monthly: Tires naturally lose 1-2 PSI per month
• Different units: Know which unit your gauge displays

Altitude Effects on Pressure

Atmospheric pressure decreases with altitude. At Denver (5,280 ft elevation), atmospheric pressure is only 12.1 PSI (0.83 bar) compared to 14.7 PSI at sea level. This affects engine performance, cooking times, and bodily functions.