Weights and measures - Pharmaceutics - I B. Pharma 1st Semester

Weights and measures

Objective

At the end of this lecture, student will be able to

• List the various systems of weights and measures

• Convert units within the various systems

• Compare the different systems

• Relate common household measurements to the imperial and metric measures

Weights and measures 

A thorough knowledge of weights and measures – to understand various types of calculations used in dispensing.

The two systems of weights and measures

The Imperial system

The Metric system

The imperial system

An old system of weights and measures

The Imperial system type:

Apothecaries system

• Avoirdupois system

1. Avoirdupois weight measures

– ‘Pound’ is the standard unit for weighing

– All measures of mass are derived from the Imperial standard pound (lb)

Avoirdupois measure of weight

Pound

Ounce

Grain

1

16

7000

 

1

437.5

2. Apothecaries weight measures

– Also known as ‘Troy’ system

– ‘Grain’ is the standard unit

Apothecaries’ measures of weight

• 20 grains = 1 scruple ()

• 3 scruples = 1 drachm/ dram (ʒ)

• 8 drachms = 1 ounce (oz )

• 12 ounces  = 1 pound (lb)

A typical set of Apothecary weight will contain the following units:

• 2 fluid ounce

• 1 fluid ounce

• 2 fluid dram

• 1 fluid dram

• ½ dram

• 2 scruple

• 1 scruple

• ½ scruple

• 5, 4, 3, 2, 1, ½ grain


Pound

Ounce

Drachm

Scruple

Grain

1

12

96

228

5760

 

1

8

24

480

 

 

1

3

60

 

 

 

1

20

Conversion table

I Lb

16 oz (avoir)

1 Lb

7000 grains

1oz

7000/16 = 473.5 grains

20 grains

1 scruple

60 grains

1 drachm

480 grains

1 ounce

12 ounce

1 pound

5760 grains

1 pound

Measurement of capacity in Imperial system

• The standard unit for capacity is ‘gallon’ in both apothecaries and avoirdupois system.

Gallon

Quart

Pint

Fluid ounce

Fluid drachm

Minim

1

4

8

128

1024

61440

 

1

2

32

256

15360

 

 

1

16

128

7680

 

 

 

1

8

480

 

 

 

 

1

60

Imperial measures for volume

60 minims () = 1 fluid drachm (fʒ)

8 fluid drachm = 1 fluid ounce (f)

16 fluid ounces = 1 pint (pt or O)

2 pints = 1 quart ( qt)

4 quarts = 1 gallon ( gal or C )

The Metric System

• Most commonly used measure of weights and measures

• The three basic units of metric system – meter, gram and litre

• Other units are formed by adding prefix to one of the basic units

• Litre and gram – most commonly used basic units in pharmacy

PREFIX

VALUE

Micro

1/10,00,000

Milli

1/1,000

Centi

1/100

Deci

1/10

Deca

10

Hecto

100

Kilo

1,000

Conversions – Imperial to Metric

IMPERIAL

METRIC

15.43 grains

1 gram

1 grain

65 mg

2.2 pounds

1 kg

16.23 minims

1 ml

1 minim

0.06 ml

1 fluid drachm

3.69 ml

1 fluid ounce

29.57 ml

1 pint

473 ml

1 gallon

3785 ml

Household / Domestic measures

Domestic measures

Metric system

Imperial system

1 drop

0.06 ml

1 minim

1 teaspoonful

4 ml/5 ml

1 fluid drachm

1 desert spoonful

8 ml/10 ml

2 fluid drachms

1 tablespoonful

15 ml

4 fluid drachms

1 wineglassful

60 ml

2 fluid ounces

1 teacupful

120 ml (4 fluid ounce)

4 fluid ounces

1 tumblerful

240 ml (8 fluid ounce)

8 fluid ounce

Summary

• Two basic systems of weights and measures – Imperial and metric

• The two imperial systems of measures – Avoirdupois and Apothecaries

• Apothecary measure of weight – Grain, scruple, drachm ounce pound

• Avoirdupois measure of weight - Grain ounce pound

• Imperial measure of volume – minim, scruple, drachm, fluid ounce pint quart

• Common household measurements

Post a Comment

0 Comments