Unit Conversion Master Guide 2026

"How many kilometers is 1 mile?" "Is 77 degrees Fahrenheit hot?" "How many GB is 1 TB?"

International travel, online shopping from abroad, software development... There are more situations requiring unit conversion than you might think. Master key unit conversions with this guide.

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Length Units

Metric System (SI)

1 km = 1,000 m = 100,000 cm = 1,000,000 mm

Imperial System (US/UK)

Key Conversion Table

Real-life Examples

Marathon distance: 42.195km = 26.2mi
Basketball court length: 28.65m = 94ft
55-inch TV: 55 × 2.54 = 139.7cm (diagonal)
Height 6 feet: 6 × 30.48 = 182.88cm

Memory Tips

• 1 inch = 2.54 cm (exact value, must memorize!)
• 1 mile ≈ 1.6 km (easy to add 10%)
• 1 foot ≈ 30 cm (actually 30.48 cm)
• Height 5'10" = 178 cm (5×30 + 10×2.5)

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Weight Units

Metric System (SI)

Imperial System

Key Conversion Table

Real-life Examples

Body weight 70kg: 70 × 2.205 = 154.3lb
Steak 8oz: 8 × 28.35 = 226.8g
International shipping limit 150lb: 150 × 0.454 = 68.1kg

Memory Tips

• 1 pound ≈ 450g (about 0.45kg)
• 1 ounce ≈ 28g (calculate as ~30g)
• kg → lb: Double and add 10%
  • 70kg → 140 + 14 = 154lb

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Temperature Units

Three Scales

Conversion Formulas

Celsius → Fahrenheit: °F = (°C × 9/5) + 32
Fahrenheit → Celsius: °C = (°F - 32) × 5/9
Celsius → Kelvin: K = °C + 273.15

Commonly Used Temperature Reference

Quick Mental Math

Celsius → Fahrenheit (approximate):

(°C × 2) + 30 ≈ °F

Example: 25°C → (25 × 2) + 30 = 80 (actual 77)

Fahrenheit → Celsius (approximate):

(°F - 30) ÷ 2 ≈ °C

Example: 80°F → (80 - 30) ÷ 2 = 25 (actual 26.7)

Daily Reference Points

Cool: 10°C = 50°F
Comfortable: 22°C = 72°F
Warm: 30°C = 86°F
Hot: 35°C = 95°F
Heat wave: 40°C = 104°F

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Data Units

Basic Units

Binary vs Decimal

Why Does Storage Appear Different?

Advertised: 1TB SSD (decimal basis)
Actual capacity: 1,000,000,000,000 B
OS display: 1,000,000,000,000 / 1,073,741,824 = 931 GB

→ "I bought 1TB but only see 931GB!" (This is normal)

Bits vs Bytes (Internet Speed)

Internet 1Gbps = 1,000 Mbps (bits)
Actual download speed = 1,000 / 8 = 125 MB/s (bytes)

100Mbps Internet
→ Maximum 12.5 MB/s download
→ 1GB file = about 80 seconds

Real-life Data Sizes

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Volume/Capacity Units

Metric System

Imperial System

Key Conversions

Real-life Examples

Soda can 355mL = 12 fl oz (US standard)
1 gallon of gas: 3.785L (US gas stations)
Cooking 1 cup: about 240mL

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Area Units

Key Conversions

Real Estate Area

1 acre = 4,047 m² = 43,560 ft²

1,000 ft² apartment = 92.9 m²
2,000 ft² house = 185.8 m²

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Speed Units

Key Conversions

Real-life Examples

Highway 100km/h = 62mph
US highway 65mph = 105km/h
Marathon world record about 21km/h = 13mph
Speed of sound 343m/s = 1,235km/h = 767mph

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Using Unit Conversion Tools

Advantages of Online Tools

• Accurate conversion (no rounding errors)
• Support for various units
• History feature
• Mobile-friendly

Unit Converter Tips

1. Paste input values: Convert even long numbers accurately
2. Reverse conversion: Switch direction with one click
3. Related unit suggestions: Check similar units together
4. Copy feature: Copy results to clipboard

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Commonly Confused Units

1. UK vs US Gallon

US gallon: 3.785 L
UK gallon: 4.546 L

Difference: about 20%!

2. Types of Tons

Metric ton (t): 1,000 kg
US ton (short ton): 907.2 kg
UK ton (long ton): 1,016 kg

3. Nautical Mile vs Mile

Nautical mile: 1.852 km
Land mile: 1.609 km

Aviation/maritime use nautical miles!

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FAQ

Q1: Why does the US use the imperial system?

A: For historical reasons, the US maintains the British measurement system. Only the US, Liberia, and Myanmar officially use the imperial system.

Q2: What are SI units?

A: International System of Units (Systeme International). Based on 7 scientifically defined base units including meter, kilogram, and second.

Q3: How do I convert clothing sizes?

A: Varies by brand, but approximately:

• US S = EU 36-38
• US shoe 7 = EU 38
• Waist 30 inches = 76cm

Q4: What about "cups" in foreign recipes?

A: US cup = about 240mL. Standard measuring cups vary by country. For precise cooking, weight (grams) is recommended.

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Conclusion

Remember these key conversions:

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