Lesson overview
Desired Over Have (D/H × Q) Dosage Calculations
Ready when you are
Start with short teaching slides, then answer the lesson questions. Your progress stays on this browser.
Learning outcomes
What you will learn
- Identify Desired, Have and Quantity in a dosage question.
- Match the dose units before calculating.
- Use D ÷ H × Q to calculate the amount to give.
- Check the answer unit and whether the result is reasonable from the supplied numbers.
Clinical connection
Why this matters
This method makes a common dosage relationship explicit and gives you a repeatable setup for tablets and liquid doses when the question supplies an ordered dose and an available strength.
Quick concept
How to use Desired ÷ Have × Quantity
Identify the ordered dose as Desired, the available dose as Have, and the amount containing that available dose as Quantity. Match the dose units before dividing, then multiply by Quantity.
Formula
Desired ÷ Have × Quantity = amount to give
Worked example
Educational example: order 500 mg; available 250 mg in 5 mL.
500 ÷ 250 × 5 = 10
Answer: 10 mL
A correct arithmetic result does not independently verify the order, product, route or administration plan. Use the current clinical information and required checks.
Lesson plan
How the lesson works
- 1
Learn
Short teaching slides explain one idea at a time with plain-language examples.
- 2
Practise
Answer calculation or scenario questions and receive immediate feedback.
- 3
Finish
Complete the lesson check and save your learning progress on this browser.
Keep going
Learn, practise, apply and check this skill
Use the page that matches what you need next. Each resource has a different job, so the lesson can stay focused on teaching the skill.
Understand
Medication Calculation Methods Guide
Compare D/H × Q, ratio/proportion and dimensional analysis on the same medication relationship.
Review
Unit Conversions lesson
Review dose-unit conversion before comparing Desired with Have.
Compare
Choosing a Calculation Method
See the same dosage problem solved three valid ways.