Ratio and proportion calculation is useful and easy to use in dosage calculation. It is allows us the ability to compare numbers, units of measurement, or values. Where ratios and proportions expressed as fractions, canceled out by cross multiplication or division.

**Equation:**

H/V = D/X or H:V :: D:X

Have on hand/Quantity you have = Desired Amount/X (Ordered dose)

**Examples**

1. A provider orders lorazepam 4 mg intravenous (IV) push for a CIWA score of 25. On hand, the clinicians has 2 mg/mL vials. How many milliliters are required to carry out the ordered dose?

Have on hand/Quantity you have = Desired Amount/X

2 mg : 1ml = 4 mg : x ml

2 mg/1 mL = 4 mg/X

2X/2 = 4/2

X = 2 mL

2. You had a medication with a dosage strength of 50 mg per 1 mL, and the prescriber orders a dosage of 25 mg. A ratio and proportion may be used to determine how many milliliters to administer.

Have on hand/Quantity you have = Desired Amount/X

50 mg / 1 ml = 25 mg / X ml

X = 0.5 ml

**Related:** Drug Dose Calculation Formula

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