Method for Increasing and Reducing Formulae

So how do you increase or reduce a formula?
Look at the following example showing how to increase a formula.
The same method is used for reducing a formula.

The source formula for Paraffin Ointment BP 1988 is:-
White Beeswax
20g
Hard Paraffin
30g
Cetosterayl Alcohol
50g
White Soft Paraffin
900g
You need to prepare 1500 g of Paraffin Ointment BP 1988. How much of each ingredient do you need?
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Find out what the source formula is eg from the British Pharmacopeia.
Find the total mass of the source formula.
Total Mass = 20 + 30 + 50 + 900 = 1000 g
Find by how much you need to increase the formula.
You need 1500 g and you know what is in 1000 g.
You need to make 1500 / 1000 times MORE of the product
ie 1.5 times more product.
You are increasing the formula by the amount :        Required Mass       
 Source Formula Mass
Multiply each part of the source formula by how much you need to increase the formula.
You need White Beeswax 20 x 1.5g = 30g
  Hard Paraffin 30 x 1.5g = 45g
  Cetostearyl Alcohol 50 x 1.5g = 75g
  White Soft Paraffin 900 x 1.5g = 1350g
Check your calculations.
Checking the Calculation
It is essential that you check your calculations. If you have made a mistake and the proportions of the chemicals have changed, you may endanger the life of the person for whom you have made the preparation.

Check the degree of the increase:
  Required increase = 1500 / 1000 = 1.5
Increase In: White Beeswax = 30 / 20 = 1.5
  Hard Paraffin = 45 / 30 = 1.5
  Cetostearyl Alcohol = 75 / 50 = 1.5
  White Soft Paraffin = 1350/900 = 1.5
Check the proportions of the chemicals:
    Source Formula Calculated Amounts
  White Beeswax 20/1000  = 0.02 30/1500 = 0.02
  Hard Paraffin 30/1000 = 0.03 45/1500  = 0.03
  Cetostearyl Alcohol 50/1000 = 0.05 75/1500 = 0.05
  White Soft Paraffin 900/1000 = 0.9 1350/1500 = 0.9
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