6. WEIGHTS AND MEASURES

Weights and Measures

For accurate drug dispensing, pharmacists must have thorough knowledge of weights and measures. Two main systems are used:

1. Imperial System
2. Metric System

1. Imperial System:

An older system of weights and measures, weight here means the gravitational force on a body proportional to its mass.

The imperial system includes two parts:

• Avoirdupois System: Used primarily for weight measurement.
• Apothecary System: Includes both volume and weight, used for compounding and preparing dilutions.

Avoirdupois System:

• 1 pound (lb) = 16 ounces (oz)
• 1 pound = 7000 grains
• 1 ounce (oz) = 437.5 grains
• 437.5 grains = 1 oz = 28.35 gm
• 7000 grains = 1 lb = 16 oz = 454 gm
• 1 kg = 2.2 lb
• 1 grain (gr) = 64.8 mg

Apothecary System:

This measures volume and weight:

• Volume:
  • 1 teaspoon (tsp) = 5 ml = 1 dram = 5 cc
  • 1 tablespoon (tbsp) = 15 ml
  • 1 fluid ounce (fl oz) = 29.57 ml
  • 1 pint (pt) = 473 ml = 16 fl oz
  • 1 quart = 946 ml = 2 pints
  • 1 gallon = 3784 ml = 8 pints = 128 fl oz
• Weight:
  • 1 grain = 64.8 mg
  • 1 ounce = 31.1 gm = 480 grains

2. Metric System:

The metric system is the preferred system in India since April 1, 1964, and is widely used globally, including in the United States. It uses prefixes like kilo-, hecto-, deka-, deci-, centi-, and milli- combined with base units (meter, liter, gram).

Measurement of Weight in Metric System

• 1 kilogram (kg) = 1000 grams (g)
• 1 gram = 1000 milligrams (mg)
• 1 milligram (mg) = 0.001 grams
• 1 microgram (mcg) = 0.000001 grams
• Other units: hectogram (100 g), decagram (10 g), decigram (0.1 g), centigram (0.01 g)

Measurement of Volume or Capacity

• 1 liter (L) = 1000 milliliters (ml)

Conversion Examples Using Ratio and Proportion

• 2,000 gr = 4.167 oz (AP)
• 500 gm = 16.077 oz (AP)
• 500 mg = 7.716 gr
• 100 fl oz = 6.25 pt
• 500 fl oz = 3.906 gal
• 4.5 oz (AP) = 139.95 gm
• 3 gr = 194.4 mg
• 20,000 ml = 5.284 gal
• 9.3 pt = 1,419 ml
• 119 ml = 4.024 fl oz
• 2.5 gal = 320 fl oz
• 5,000 gr = 10.417 oz (AP)
• 25 pt = 3.125 gal
• 1,500 ml = 3.171 pt
• 6 fl oz = 177.42 ml
• 0.75 gal = 2,838.75 ml
• 1,000 gr = 2.083 oz (AP)
• 3.25 gal = 26 pt
• 350 gr = 22,680 mg
• 2.5 oz (AP) = 1,200 gr
• 1.5 tsp = 7.5 ml
• 12.5 ml = 2.5 tsp
• 1.5 fl oz = 44.355 ml
• 375 ml = 12.682 fl oz
• 24 fl oz = 1.5 pt
• 275 gm = 8.842 oz (AP)
• 500 ml = 33.333 tbsp
• 1 drop = 0.05 ml
• 1 tsp = 5 ml
• 1 tbsp = 15 ml
• 1 wineglass full = 60 ml
• 1 tumbler full = 240 ml
• 1 inch = 2.54 cm
• 1 pint = 473 ml
• 1 gallon = 3785 ml
• 1 quart = 946 ml

Detailed Notes:

For PDF style full-color notes, open the complete study material below: