Introduction
I often come across books, recipes, or resources that use both the US System and the Metric System. Since I’m not very familiar with the US System, I created this page as a quick and easy reference for myself—and to share with friends who might find it useful.
This summary was prepared with the help of ChatGPT by OpenAI, and all values and conversions are based on standard public domain sources, primarily Newell & Tiesinga (2019) and Poids et Mesures (2024). Please verify values if you intend to use them for scientific or professional purposes.
Systems Overview
US System
The US System is primarily used in the United States and relies on a set of non-decimal units.
Length
| Inch |
in |
Base unit |
| Foot |
ft |
12 inches |
| Yard |
yd |
3 feet |
| Mile |
mi |
5,280 feet |
Weight (Mass)
| Ounce |
oz |
Base unit |
| Pound |
lb |
16 ounces |
| Ton |
tn |
2,000 pounds |
Volume (Liquid)
| Teaspoon |
tsp |
Base unit |
| Tablespoon |
tbsp |
3 teaspoons |
| Cup |
c |
8 fluid ounces |
| Pint |
pt |
2 cups |
| Quart |
qt |
2 pints |
| Gallon |
gal |
4 quarts |
Temperature
- Degrees Fahrenheit (°F)
- Water freezes at 32°F
- Boils at 212°F
Time
| Second |
s |
Base unit |
| Minute |
min |
60 seconds |
| Hour |
hr |
60 minutes |
| Day |
— |
24 hours |
Metric System
The Metric System is used globally and follows a decimal structure based on powers of 10.
Prefixes
| milli |
m |
10⁻³ |
0.001 |
| centi |
c |
10⁻² |
0.01 |
| deci |
d |
10⁻¹ |
0.1 |
| (base) |
— |
10⁰ |
1 |
| deka |
da |
10¹ |
10 |
| hecto |
h |
10² |
100 |
| kilo |
k |
10³ |
1,000 |
| mega |
M |
10⁶ |
1,000,000 |
| giga |
G |
10⁹ |
1,000,000,000 |
Length
| Millimetre |
mm |
0.001 meter |
| Centimetre |
cm |
0.01 meter |
| Decimetre |
dm |
0.1 meter |
| Meter |
m |
Base unit |
| Decametre |
dam |
10 meters |
| Hectometre |
hm |
100 meters |
| Kilometre |
km |
1,000 meters |
Mass (Weight)
| Milligram |
mg |
0.001 gram |
| Centigram |
cg |
0.01 gram |
| Decigram |
dg |
0.1 gram |
| Gram |
g |
Base unit |
| Decagram |
dag |
10 grams |
| Hectogram |
hg |
100 grams |
| Kilogram |
kg |
1,000 grams |
| Metric Ton |
t |
1,000 kilograms |
Volume
| Millilitres |
mL |
0.001 litres |
| Centilitres |
cL |
0.01 litres |
| Decilitres |
dL |
0.1 litres |
| Litres |
L |
Base unit |
| Decalitres |
daL |
10 litres |
| Hectolitres |
hL |
100 litres |
| Kilolitres |
kL |
1,000 litres |
Temperature
- Degrees Celsius (°C)
- Water freezes at 0°C, boils at 100°C
- Kelvin (K)
- Scientific use; absolute zero starts at 0 K
Time
Same as the US System.
| Second |
s |
Base unit |
| Minute |
min |
60 seconds |
| Hour |
hr |
60 minutes |
| Day |
— |
24 hours |
Side-by-Side Comparison
Length
| Small Unit |
1 inch |
2.54 cm |
| Medium Unit |
1 foot = 12 inches |
0.3048 meters |
| Large Unit |
1 mile = 5,280 feet |
1.609 kilometres |
Mass (Weight)
| Small Unit |
1 ounce |
28.35 grams |
| Medium Unit |
1 pound = 16 ounces |
0.4536 kilograms |
| Large Unit |
1 ton = 2,000 pounds |
907.18 kilograms |
Volume
| Small Unit |
1 teaspoon |
4.93 millilitres |
| Medium Unit |
1 cup = 8 fl oz |
236.59 millilitres |
| Large Unit |
1 gallon |
3.785 litres |
Temperature
| US (°F) |
32°F |
212°F |
°C = (°F - 32) × 5⁄9 |
| Metric (°C) |
0°C |
100°C |
°F = (°C × 9⁄5) + 32 |
Summary
US System
- Primarily used in the United States
- Based on historical and customary units
- Common in daily life, especially in the US
Metric System
- Used worldwide
- Decimal-based and easy to convert
- Preferred for scientific and international contexts