Here is a short list of ballpark equivalents that are fairly easy to remember. Keep in mind these are only ballpark estimates and are purposefully kept to round numbers. So only use these for quick mental calculations and don't go building spaceships or anything with them.
- 1 cup of water ~ 0.5 pounds
- 1 pound ~ 0.5 kilograms
- 1 kilometer ~ 0.5 mile
- 1 gallon ~ 5 liter
- 1 liter ~ 5 cups
- 1 teaspoon ~ 5 milliliters
- 1 meter ~ 1 yard
- 1 centimeter ~ 0.5 inch
- 1 atmosphere ~ 10 psi
- 1 horsepower ~ 1000 Watts
- 1 BTU ~ 1000 Joules
- 1 food calorie ~ 5000 Joules
- 1 gallon gas ~ 100 million Joules
- 1 square meter of solar light ~ 1000 Watts
- 1 Joule ~ lift 1 pound 1 foot
- 1 Joules heat ~ heat 1 gram air +1'C
- 5 Joules heat ~ heat 1 gram water +1'C
- 10 Joules ~ lift 1 kilogram 1 meter
- speed of sound ~ 1000 feet per second
- speed of light ~ 1 billion feet per second
