Looking at units system for ERP system recently, and this clarification came about:
Common non-SI units and their capitalization:
- gal = gallon (lowercase)
- qt = quart (lowercase)
- pt = pint (lowercase)
- fl oz = fluid ounce (lowercase)
- lb = pound (lowercase)
- oz = ounce (lowercase)
Generally, unit abbreviations are lowercase unless:
- They’re derived from a proper name (like Newton = N, Watt = W, Pascal = Pa)
- They could be confused with numbers or other symbols (like L for liter)
So for standard US customary/imperial units: almost all are lowercase.
Almost all standard non-SI units are lowercase:
US Customary/Imperial:
- gal (gallon)
- qt (quart)
- pt (pint)
- fl oz (fluid ounce)
- lb (pound)
- oz (ounce)
Exceptions (derived from proper names):
- N = Newton (force)
- W = Watt (power)
- Pa = Pascal (pressure)
- C = Celsius (temperature)
- F = Fahrenheit (temperature)
Rule: Standard unit abbreviations are lowercase UNLESS derived from a proper name or could be confused with a number (like L for liter).