Drug Dosage Calculations
Abbreviations Commonly Used in Dosage
Abbreviation Te rm
po by mouth (or orally)
susp suspension
pm as needed
tab tablet
cap capsule
q every
bid twice a day
tid three times a day
qid four times a day
The basic drug dosage fonmu l a listed below can be used for most drug dosage
calculations. These calcu llations are necessary when a doctor orders a particular desired
dose of medication and the medication you have avai lable on hand is in the form of
mass/tablet or mass/volume.
Formula:
D Desired
- XQ = X --- X Quantity =X
H Have
Term Symbol Meaning Example
"Give 500 milligrams"
Dosage ordered or The amount of medication that
D "Give grains/v"
desired dose the physician prescribed "Give 1.2 milliliters"
The amount of drug in a
Dosage strength or 250 milligrams
H specific unit of measure (what
supply on hand Grains/v
is available; in stock)
The unit of measure for the per 2 milliliters
Unit of measure or
Q specific dosage strength or per capsule
quantity of unit
supply on hand per tablet
The dosage you are trying to
Unknown Dosage X Not applicable
calculate
©Tutoring and Learning Centre, George Brown College, 2020 | www.georgebrown.ca/tlc
Abbreviations Commonly Used in Dosage
Abbreviation Te rm
po by mouth (or orally)
susp suspension
pm as needed
tab tablet
cap capsule
q every
bid twice a day
tid three times a day
qid four times a day
The basic drug dosage fonmu l a listed below can be used for most drug dosage
calculations. These calcu llations are necessary when a doctor orders a particular desired
dose of medication and the medication you have avai lable on hand is in the form of
mass/tablet or mass/volume.
Formula:
D Desired
- XQ = X --- X Quantity =X
H Have
Term Symbol Meaning Example
"Give 500 milligrams"
Dosage ordered or The amount of medication that
D "Give grains/v"
desired dose the physician prescribed "Give 1.2 milliliters"
The amount of drug in a
Dosage strength or 250 milligrams
H specific unit of measure (what
supply on hand Grains/v
is available; in stock)
The unit of measure for the per 2 milliliters
Unit of measure or
Q specific dosage strength or per capsule
quantity of unit
supply on hand per tablet
The dosage you are trying to
Unknown Dosage X Not applicable
calculate
©Tutoring and Learning Centre, George Brown College, 2020 | www.georgebrown.ca/tlc
