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 |
Fluid |
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 |
Metric |
Imperial |
|
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