US customary and British Imperial systems share some familiar names, but certain units represent different quantities.
The underlying idea
International inches and feet have exact metric definitions. Gallons require a system label. Recipes also vary in cup definitions, which this site does not currently convert.
Identify the system first
International inches and feet have exact metric definitions. Gallons require a system label. Recipes also vary in cup definitions, which this site does not currently convert. Choose measurements that describe the same object, system, or period; changing the reference changes what the result means.
Worked example
A US liquid gallon is about 3.785 liters. An Imperial gallon is about 4.546 liters, so the word gallon alone is ambiguous.
Put the method into practice
- Write down the quantity you need to find.
- Identify the measurements and their units.
- Convert units before doing the calculation.
- Apply the formula and keep unrounded intermediate values.
- Check whether the result is reasonable for your situation.
Try the Volume Converter with your own values.
Common mistakes
Mixing units, using the wrong reference value, and rounding too early can all change the result. A calculator cannot repair inaccurate measurements. For project estimates, distinguish the calculated base quantity from allowances and supplier rounding.
What to learn next
Explore this topic’s related answers below for focused examples and alternative ways to check a result.
Sources & references
- NIST Guide to the SI: Conversion Factors — National Institute of Standards and Technology
