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Unit Conversion Formulas Reference | ConversionCalculator.net

Unit Conversion Formulas

Comprehensive reference guide for accurate unit conversion formulas across all measurement categories, sourced from international standards

📋 Formula Categories

Pressure Conversion Formulas

Pressure conversions are fundamental in engineering, meteorology, and medical applications. All formulas are based on Pascal (Pa) as the SI base unit.

Pascal ↔ PSI (Pounds per Square Inch)
PSI = Pa ÷ 6,894.757
Pa = PSI × 6,894.757
Conversion factor: 1 PSI = 6,894.757 Pa (exact)
Pascal ↔ Bar
Bar = Pa ÷ 100,000
Pa = Bar × 100,000
Conversion factor: 1 Bar = 100,000 Pa (exact)
Pascal ↔ Atmosphere (atm)
atm = Pa ÷ 101,325
Pa = atm × 101,325
Standard atmospheric pressure: 1 atm = 101,325 Pa (exact)
Pascal ↔ mmHg (Torr)
mmHg = Pa ÷ 133.322
Pa = mmHg × 133.322
Based on mercury density at 0°C: 1 mmHg = 133.322 Pa
Example: Convert 50 PSI to Bar
Step 1: Convert PSI to Pascal: 50 × 6,894.757 = 344,737.85 Pa
Step 2: Convert Pascal to Bar: 344,737.85 ÷ 100,000 = 3.45 Bar

Pressure Unit Relationships

From Unit To Unit Multiply By Application
PSI Bar 0.0689476 Automotive, industrial
Bar PSI 14.5038 US engineering conversion
kPa PSI 0.145038 Metric to imperial
mmHg kPa 0.133322 Medical applications

Temperature Conversion Formulas

Temperature conversion requires both multiplication factors and offset additions due to different zero points between scales.

Celsius ↔ Fahrenheit
°F = (°C × 9/5) + 32
°C = (°F – 32) × 5/9
Remember: multiply first, then add/subtract offset
Celsius ↔ Kelvin
K = °C + 273.15
°C = K – 273.15
Kelvin is absolute temperature scale; 0K = -273.15°C
Fahrenheit ↔ Rankine
°R = °F + 459.67
°F = °R – 459.67
Rankine is absolute scale using Fahrenheit degrees
Kelvin ↔ Rankine
°R = K × 9/5
K = °R × 5/9
Direct conversion between absolute scales

🌡️ Temperature Reference Points

  • Absolute Zero: 0K = -273.15°C = -459.67°F = 0°R
  • Water Freezing: 273.15K = 0°C = 32°F = 491.67°R
  • Water Boiling: 373.15K = 100°C = 212°F = 671.67°R
  • Human Body: 310.15K = 37°C = 98.6°F = 558.27°R

Length & Distance Conversion Formulas

Length conversions between metric and imperial systems, with exact and derived relationships.

Metric System (Base: Meter)
km = m ÷ 1,000
cm = m × 100
mm = m × 1,000
Metric system uses powers of 10
Imperial System
ft = in ÷ 12
yd = ft ÷ 3
mi = ft ÷ 5,280
Imperial relationships are historical, not systematic
Metric ↔ Imperial (Exact)
cm = in × 2.54
in = cm ÷ 2.54
International inch definition: 1 in = 2.54 cm (exact)
Large Distance Conversions
km = mi × 1.609344
mi = km × 0.621371
Derived from inch definition: 1 mi = 1.609344 km (exact)
Example: Convert 6 feet 3 inches to centimeters
Step 1: Convert to total inches: (6 × 12) + 3 = 75 inches
Step 2: Convert to centimeters: 75 × 2.54 = 190.5 cm

Weight & Mass Conversion Formulas

Mass conversion formulas for everyday and scientific applications. Note: weight and mass are technically different but often used interchangeably.

Kilogram ↔ Pound
lb = kg × 2.20462
kg = lb ÷ 2.20462
International avoirdupois pound: 1 lb = 0.45359237 kg (exact)
Gram ↔ Ounce
oz = g × 0.035274
g = oz × 28.3495
Avoirdupois ounce: 1 oz = 28.349523125 g (exact)
Metric System
kg = g ÷ 1,000
g = mg × 1,000
tonne = kg ÷ 1,000
Metric mass units follow powers of 10
Large Mass Units
short ton = lb ÷ 2,000
long ton = lb ÷ 2,240
metric tonne = kg ÷ 1,000
Different ton definitions: US, UK, and metric

Weight vs. Mass Distinction

⚖️ Technical Definitions

  • Mass: Amount of matter (kg, g, slug)
  • Weight: Force due to gravity (N, lbf)
  • Earth Weight Formula: Weight = Mass × 9.80665 m/s²
  • Common Usage: “Weight” often refers to mass in daily life

Volume & Capacity Conversion Formulas

Volume conversions for liquids, gases, and bulk materials across metric and imperial systems.

Metric Volume (Base: Liter)
mL = L × 1,000
m³ = L ÷ 1,000
cm³ = mL × 1
1 liter = 1,000 cm³ = 0.001 m³
US Liquid Volume
gal = qt ÷ 4
qt = pt ÷ 2
pt = cup ÷ 2
US gallon = 231 cubic inches (exact)
Metric ↔ US Volume
L = US gal × 3.78541
mL = fl oz × 29.5735
L = US qt × 0.946353
Based on US gallon = 231 in³
Imperial vs US Volume
Imp gal = US gal × 1.20095
Imp fl oz = US fl oz × 0.96076
Imperial gallon = 4.54609 L; US gallon = 3.78541 L
Example: Convert 2.5 liters to US gallons
US gallons = 2.5 L ÷ 3.78541 = 0.660 gallons

Cooking Measurement Conversions

Unit Milliliters (mL) US Equivalent Notes
1 teaspoon 4.92892 1/3 tablespoon Often rounded to 5 mL
1 tablespoon 14.7868 3 teaspoons Often rounded to 15 mL
1 cup 236.588 16 tablespoons Often rounded to 240 mL

Speed & Velocity Conversion Formulas

Speed and velocity conversions for automotive, aviation, and scientific applications.

Common Speed Conversions
km/h = mph × 1.60934
m/s = km/h ÷ 3.6
knots = km/h ÷ 1.852
Based on exact definitions of mile and nautical mile
Scientific Units
m/s = ft/s × 0.3048
km/s = m/s ÷ 1,000
c = 299,792,458 m/s
Speed of light in vacuum (exact definition)
Aviation & Maritime
knots = mph × 0.868976
Mach = speed ÷ speed_of_sound
Nautical mile = 1,852 m (exact); Mach depends on conditions
Quick Conversions
mph ≈ m/s × 2.24
km/h ≈ m/s × 3.6
Approximate conversions for quick estimation

Physical Constants for Conversions

Fundamental physical constants used in unit conversions and scientific calculations.

🔬 Universal Constants

  • Speed of light in vacuum: c = 299,792,458 m/s (exact)
  • Planck constant: h = 6.62607015 × 10⁻³⁴ J⋅s (exact)
  • Elementary charge: e = 1.602176634 × 10⁻¹⁹ C (exact)
  • Avogadro constant: Nₐ = 6.02214076 × 10²³ mol⁻¹ (exact)

🌍 Earth & Standard Conditions

  • Standard gravity: g = 9.80665 m/s² (exact)
  • Standard atmosphere: 101,325 Pa (exact)
  • Standard temperature: 273.15 K = 0°C (exact)
  • Molar gas constant: R = 8.314462618 J/(mol⋅K) (exact)

📏 Defining Relationships

  • International inch: 1 in = 2.54 cm (exact)
  • International pound: 1 lb = 0.45359237 kg (exact)
  • Nautical mile: 1 nmi = 1,852 m (exact)
  • International calorie: 1 cal = 4.184 J (exact)

Source Standards

All conversion factors and constants are sourced from:

  • NIST (National Institute of Standards and Technology) – US measurement standards
  • BIPM (International Bureau of Weights and Measures) – International SI standards
  • CODATA – Committee on Data for Science and Technology
  • ISO (International Organization for Standardization) – International standards

Formula Usage Guidelines

🎯 Accuracy and Precision

  • Exact vs. Approximate: Some conversions are exact definitions (1 in = 2.54 cm), others are measured values
  • Significant Figures: Match the precision of your input data; don’t claim false precision
  • Rounding: Round final answers appropriately for your application

🔄 Order of Operations

  • Temperature: Always apply multiplication before addition/subtraction
  • Complex Units: Convert numerator and denominator separately (e.g., m/s to ft/min)
  • Chain Conversions: Use intermediate steps to avoid compounding errors

⚠️ Common Formula Mistakes

  • Temperature Offset: Forgetting to add/subtract 32 or 273.15
  • Imperial Variations: US vs. Imperial gallons, different ton definitions
  • Unit Confusion: Mass vs. weight, volume vs. capacity
  • Precision Errors: Using too few decimal places in conversion factors
Best Practice Example: Converting 75°F to Celsius
❌ Wrong: 75 × 5/9 + 32 = 73.67°C
✅ Correct: (75 – 32) × 5/9 = 23.89°C
Always follow the correct order: subtract offset first, then multiply

Important Disclaimer

⚠️ Educational and Reference Use Only

Medical Information: Any formulas, conversion factors, or references related to medical measurements (blood pressure, body temperature, etc.) are provided for educational purposes only and are not intended as medical advice, diagnosis, or treatment recommendations.

Professional Medical Consultation: Never use these conversion formulas for medical decisions, diagnostic procedures, or treatment planning. Always consult qualified healthcare professionals for any medical measurements or calculations.

Critical Applications: For engineering, scientific research, medical practice, or safety-critical applications, always verify formulas and conversion factors using authoritative sources and professional-grade references. Consult with qualified professionals in your specific field.

Formula Accuracy: While all formulas are based on internationally recognized standards (NIST, BIPM, CODATA), users are responsible for verifying the appropriateness and accuracy of these formulas for their specific applications and requirements.

Limitation of Liability: ConversionCalculator.net and its contributors disclaim any liability for consequences arising from the use of these formulas or conversion factors in any application.

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