Common Unit Conversion Mistakes and How to Avoid Them
Avoid costly unit conversion errors in cooking, travel, and science with these practical tips and examples.
Unit conversion mistakes have caused everything from baking disasters to spacecraft crashes. Here is how to get them right every time.
Famous Conversion Failures
Mars Climate Orbiter (1999)
NASA lost a $125 million spacecraft because one team used metric units while another used imperial. The orbiter entered the atmosphere at the wrong angle and disintegrated.
Gimli Glider (1983)
An Air Canada flight ran out of fuel mid-flight because ground crew calculated fuel in pounds instead of kilograms, loading only half the needed amount.
Kitchen Conversion Pitfalls
Volume vs. Weight
- 1 cup of flour ≠ 1 cup of sugar (by weight)
- Flour: 1 cup ≈ 125g
- Sugar: 1 cup ≈ 200g
- Butter: 1 cup ≈ 227g
Temperature
- Fahrenheit to Celsius: (°F - 32) × 5/9
- Common oven temps: 350°F = 175°C, 400°F = 205°C, 450°F = 230°C
Travel Conversions
Speed
- 60 mph ≈ 97 km/h
- Quick estimate: multiply km/h by 0.6 for mph
Distance
- 1 mile ≈ 1.6 km
- Quick trick: use Fibonacci numbers — 5 miles ≈ 8 km, 8 miles ≈ 13 km
Fuel Economy
- mpg to L/100km: divide 235 by the mpg value
- 30 mpg ≈ 7.8 L/100km
Tips to Avoid Mistakes
1. Always state your units: Never write just "5" — write "5 kg" or "5 lbs"
2. Double-check with estimation: Does the answer make sense?
3. Use a calculator: Our [Unit Converter](/en/unit-converter) eliminates manual errors
4. Learn anchor points: Memorize a few key conversions as reference points