How do I convert gallons to liters?

1 US gallon = 3.785 liters. Multiply gallons by 3.8 for a quick estimate. Note that a UK (imperial) gallon is larger: 1 UK gallon = 4.546 liters. When renting a car in Europe and filling up at a pump measured in liters, 1 US gallon ≈ 3.8 L and 1 UK gallon ≈ 4.5 L.

International Travel Unit Conversions: Temperature, Distance, Weight & Speed

Q: How do I quickly convert Celsius to Fahrenheit in my head?

The quick mental math trick: double the Celsius temperature and add 30. For example, 20°C × 2 = 40 + 30 = 70°F (exact: 68°F). The error is within 2°F for typical weather temperatures, which is more than accurate enough for everyday use. For exact results, use the formula °F = (°C × 9/5) + 32.

Q: How do I convert my luggage weight from kg to pounds?

Multiply kg by 2.205 to get pounds. Quick mental math: double the kg value and add 10%. So 23 kg × 2 = 46 + 2.3 = 48.3 lbs (exact: 50.7 lbs). Most airlines set carry-on limits at 7 kg (15.4 lbs) and checked bag limits at 23 kg (50.7 lbs) or 32 kg (70.5 lbs) for business class.

Traveling between countries that use different measurement systems — metric vs. imperial — means decoding speed limits in km/h, grocery weights in grams, and temperatures in Celsius. This guide covers every unit conversion a traveler needs, with exact formulas and quick mental shortcuts for when you don’t have a calculator handy.

Temperature: Fahrenheit ↔ Celsius

The United States, Belize, and the Cayman Islands use Fahrenheit. Virtually everywhere else uses Celsius.

Exact formulas:

°F to °C: subtract 32, then multiply by 5/9
°C to °F: multiply by 9/5, then add 32

Mental math shortcut (°C to °F): Double the Celsius value and add 30. The error is within 2°F for typical weather ranges, which is accurate enough for packing decisions.

Celsius	Fahrenheit	What it feels like
−10°C	14°F	Very cold, heavy coat
0°C	32°F	Freezing point of water
10°C	50°F	Cool, light jacket
20°C	68°F	Comfortable spring day
30°C	86°F	Hot, t-shirt weather
40°C	104°F	Extreme heat

Use our free Temperature Converter for exact values.

Distance: Miles ↔ Kilometers

The US, UK, and a handful of other countries use miles for road distances. The rest of the world uses kilometers.

Exact factor: 1 mile = 1.609344 km. 1 km = 0.621371 miles.

Mental shortcut: Multiply miles by 1.6 (or use the Fibonacci trick: miles and km appear consecutively in the Fibonacci sequence — 5, 8, 13, 21, 34... so 5 miles ≈ 8 km, 13 miles ≈ 21 km).

Miles	Kilometers	Context
1 mi	1.61 km	Short walk (~20 min)
5 mi	8.05 km	Common 5-mile/8-km run
60 mph	96.6 km/h	Highway speed limit (US)
100 mi	160.9 km	Day road trip

Weight: Pounds & Ounces ↔ Kilograms & Grams

Luggage limits at airports are almost always posted in kilograms outside the US. Body weight is measured in pounds in the US and in stones (1 stone = 6.35 kg) in the UK.

Exact factors: 1 lb = 0.453592 kg. 1 kg = 2.20462 lbs. 1 oz = 28.3495 g.

Common airport limits:

Carry-on: 7 kg = 15.4 lbs (most airlines)
Checked bag: 23 kg = 50.7 lbs (economy); 32 kg = 70.5 lbs (business)

Use our Weight & Mass Converter to check your bag before you head to the airport.

Speed: mph ↔ km/h

Speed limits in Europe, Asia, and most of the world are in km/h. The US, UK, and a few others use mph.

Key conversions:

30 mph = 48.3 km/h (residential speed limit, US/UK)
60 mph = 96.6 km/h (rural road)
70 mph = 112.7 km/h (motorway/freeway)
100 km/h = 62.1 mph (motorway, much of Europe)
130 km/h = 80.8 mph (autobahn, French autoroute)

Fuel: Gallons ↔ Liters

Fuel is sold in liters nearly everywhere except the US (gallons) and UK (where fuel prices are displayed per liter but older habit says “miles per gallon” for fuel economy).

Exact factors: 1 US gallon = 3.785 liters. 1 UK gallon = 4.546 liters.

When renting a car in Europe and budgeting fuel costs, multiply the tank size in liters by the price per liter. A 50-liter tank (typical small car) at €1.80/L = €90 to fill up.

Clothing Sizes

Clothing sizes vary wildly by country and brand — there’s no mathematical conversion, only lookup tables. When shopping abroad, always try before you buy or consult the retailer’s specific size guide. The most common conversions for reference: US size 8 = UK size 12 = EU size 40 for women’s clothing; US shoe 10 = UK 9.5 = EU 44 for men.

Frequently Asked Questions

How do I quickly convert Celsius to Fahrenheit in my head?

Double the Celsius temperature and add 30. For example, 20°C × 2 = 40 + 30 = 70°F (exact: 68°F). The error is within 2°F for typical weather temperatures — accurate enough for deciding what to pack.

How many km is a mile?

1 mile = 1.609344 km exactly. A quick mental shorthand: multiply miles by 1.6. So 60 mph = 96 km/h, a 5-mile run = 8 km, and 100 miles = 161 km. Going the other way, multiply km by 0.625 (roughly 5/8) to get miles.

How do I convert my luggage weight from kg to pounds?

Multiply kg by 2.2 to get a close approximation. So 23 kg × 2.2 = 50.6 lbs (exact: 50.7 lbs). Most airlines allow 23 kg (50.7 lbs) for economy checked bags.

Is a UK gallon the same as a US gallon?

No. 1 US gallon = 3.785 liters; 1 UK (imperial) gallon = 4.546 liters. A UK gallon is about 20% larger. This matters when comparing fuel economy: a car rated at 30 mpg (US) gets about 36 mpg (UK) even though nothing changed about the car.

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Accuracy note: Conversion factors on SwiftConvertHub are sourced from NIST and IEC standards. Results are accurate for general use. For safety-critical or professional applications, verify results independently. Full disclaimer →

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Written by

Victor A. Calvo S.

Victor A. Calvo S. is a software engineer and digital entrepreneur who builds practical, free tools for developers, students, and professionals worldwide. He is the creator of SwiftConvertHub, InstantLinkHub, and Feexio. All conversion factors are cross-referenced against NIST and IEC standards. Learn more →