Imperial Weight Measurement Systems

Weights and Measures

• There are two main systems of weights and measures: the Imperial System and the Metric System.

The Imperial System

• This system is an older system of weights and measures.
• It includes units like inches, ounces, feet, pounds, cups, gallons, miles, and tons.
• Weight measures the gravitational force on a body and is proportional to its mass.
• The imperial system has two variations: Avoirdupois and Apothecary.

Avoirdupois System

• A measurement system of weights that uses pounds and ounces as units.
• In this system, the pound (lb) is the standard unit of weight.
• 1 pound avoir (lb) equals 16 ounces (oz).
• 1 pound avoir (lb) also equals 7000 grains (gr).

Apothecary or Troy System

• The apothecary system originated as a system for dispensing and prescribing medications.
• In this system, the grain (gr) is the standard unit of weight(mass).
• 1 pound apoth (lb) equals 12 ounces.
• 1 pound apoth (lb) also equals 5760 grains.

Measurements of Volumes

• 1 gallon (c) equals 4 quarts.
• 1 quart equals 2 pints.
• 1 pint equals 20 fluid ounces.
• 1 fluid ounce equals 8 fluid drachms.
• 1 fluid drachm equals 3 fluid scruples.
• 1 fluid scruple equals 20 minims.

The Metric System

• A system of measurement invented by the French in 1790.
• Also called the International System of Units and is the most used system of measurement on earth.
• Common units include:
  • Length: Meter
  • Volume: Liter
  • Weight: Kilogram

Measure of Length

• 1 meter (1m) equals 100 centimeters.
• 1 meter (1m) equals 1000 millimeters.
• 1 meter (1m) equals 1,000,000 micrometers.
• 1 meter (1m) equals 1,000,000,000 nanometers.

Measure of Volume

• 1 liter (L) equals 1000 milliliters.
• 1 liter (L) equals 1,000,000 microliters (µL).

Measure of Weight

• 1 gram (g) equals 1000 milligrams (mg).
• 1 gram (g) equals 1,000,000 micrograms (µg).

Percentage Solutions

• A percentage is the number of parts per 100.
• The concentration of a substance can be expressed in three types of percentages:
  • Weight in volume (w/v): grams of active ingredient in 100 ml of liquid.
  • Weight in weight (w/w): grams of active ingredient in 100 g of mixture.
  • Volume in volume (v/v): ml volume of active ingredient in 100 ml of liquid.
• In each case, concentration in percentage is calculated as the fraction of the volume/weight of the solute related to the total volume/weight of the solution.

Weight in Volume (w/v)

• Solute: 1 part by weight
• Solvent: 100 parts by volume
• The general formula for 1% (w/v) is:
  • Solute: 1 g
  • Solvent: up to 100 ml

Example 1

• To calculate the amount of potassium permanganate needed to prepare 250mL of a 0.02%(mg/mL) solution, use a proportion.
• 0. 02% means 0.02 mg in 100 ml, so x mg is needed for 250 ml.
• X = (250 x 0.02) / 100, which equals 0.05 mg.

Example 2

• To determine how many milligrams of neomycin are in 50 ml of a 1% mg/ml neomycin solution, set up a proportion.
• If every 100 ml of the solution contains 1 mg of neomycin, then x mg is in 50 ml
• X= (50×1)/100 = 0.5mg

Weight in Weight (w/w)

• Solute: 1 part by weight
• Solvent: 100 parts by weight
• The general formula for 1% (w/w) is:
  • Solute: 1 g
  • Solvent: up to 100 g

Example

• 20 g of NaCl added to enough sand to make 200 g of mixture results in a 10% (w/w) NaCl/sand mixture.

Volume in Volume (v/v)

• Solute: 1 part by volume
• Solvent: 100 parts by volume
• Formula for 1% (v/v):
  • Solute: 1 ml
  • Solvent: up to 100 ml

Example

• To find out how many ml of liquid phenol should be used to prepare 240 ml of 2.5% liquid phenol in calamine lotion, use a proportion.
• If there are 2.5 ml of liquid phenol in 100 ml, then x ml is needed for 240 ml.
• X = (2.5 x 240) / 100, which equals 6 ml.

Conversion Table

• 1 drop (domestic) = 0.06ml (metric) = 1 minim (imperial).
• 1 teaspoonful (domestic) = 5 ml (metric) = 1 fluid drachm (imperial).
• 1 desert spoonful (domestic) = 8 ml (metric) = 2 fluid drachm (imperial).
• 1 tablespoonful (domestic) = 15 ml (metric) = 4 fluid drachms (imperial).
• 1 wineglassful (domestic) = 60 ml (metric) = 2 fluid ounces (imperial).
• 1 teacupful (domestic) = 120 ml (metric) = 4 fluid ounces (imperial).
• 1 tumblerful (domestic) = 240ml (metric) = 8 fluid ounces (imperial).

Weight Measure Conversion

• 1 kg equals 2.2 pounds (lb).
• 1 ounce apoth equals 30 g.
• 1 pound avoir equals 450 g.
• 1 grain equals 65 mg.

Conversion Equivalents Weight Table

• 1 gram (g) = 15.432 grains (gr)
• 1 kilogram (kg) = 2.20 pounds (Avoir)
• 1 grain = 64.8 mg (65 or 60 mg)
• 1 ounce (oz) (Avoir) = 28.35 grams
• 1 ounce (℥) (Apoth) = 31.1 grams
• 1 pound (Avoir) = 454 grams
• 1 pound (Apoth) = 373 grams
• 1 pound (Avoir) = 7000 grains
• 1 pound (lb) (Apoth) = 5760 grains
• 1 grain Apothecary = 1 grain Avoirdupois

Example

• A prescription needs a dose of 30 grains of a drug.
• To convert to grams: 1 grain = 65mg.
• Therefore, 30 grains = 30 x 65 = 1950mg = 2g.

Example

• If 5 fluid ounces of a liquid is needed, convert to ml.
• 1 fl oz = 30 ml, so 5 fl oz = 5 x 30 = 1500 ml.

Example

• To convert a patient's weight of 12 stones 6 pounds to kg: 1 stone = 14 lb.
• First, calculate total weight in pounds: (12 x 14) + 6 = 174 lb.
• Then, convert to kg: 1kg = 2.2lb, so 174/2.2 = 79.01 kg.