When should I use this formula?

Use this formula whenever the ordered dose is different from the available medication strength. For example, if a doctor orders 750mg but you only have 250mg tablets, use D/H × Q to find you need 3 tablets.

What if my units don't match?

The Desired and Have units must match (both in mg, both in mcg, etc.). If they don't match, convert one to match the other first. For example, convert 1g to 1000mg before calculating.

Can I use this for IV medications?

Yes, this formula works for IV medications. The Quantity would be the volume that contains the Have amount. For example, if you have 100mg in 10mL, and need 40mg, the calculation is (40÷100)×10 = 4mL.

General Dose Math

Dosage Calculation Calculator (Nursing Formula)

Calculate medication doses using the nursing formula: Desired/Have × Quantity. Perfect for nursing students and healthcare professionals.

Dosage Calculator

Calculate medication doses using the nursing formula: Desired/Have × Quantity. Perfect for nursing students and healthcare professionals.

Desired Dose (D)The dose ordered/prescribed

Have/Available (H)The strength of medication on hand

Quantity/Vehicle (Q)Volume or units per dose on hand (e.g., 5mL, 1 tablet)

This calculator provides mathematical estimates only. Always verify dosages with a qualified healthcare professional before administering any medication.

Important Disclaimer

This calculator provides estimates for informational purposes only. Always consult a healthcare professional before making medical decisions.

About This Calculator

The Desired/Have × Quantity formula (also known as D/H × Q or the nursing formula) is the most widely taught method for calculating medication doses. This calculator helps nursing students, nurses, and other healthcare professionals quickly determine how much medication to administer when the ordered dose differs from the available strength.

How It Works

The formula is: Amount to Give = (Desired ÷ Have) × Quantity. Enter the desired (ordered) dose, the strength you have available, and the quantity (volume or number of units) that strength comes in. For example: Doctor orders 500mg, you have 250mg/5mL. Calculation: (500 ÷ 250) × 5 = 10mL.

Frequently Asked Questions

D/H × Q stands for Desired over Have times Quantity. It's a simple formula used to calculate medication doses: Amount = (Desired Dose ÷ Available Strength) × Quantity per unit. It works for tablets, liquids, and injectable medications.

Clinical Review

Dr. Igor I. Bussel, MD

Board-Certified Ophthalmologist

Dr. Igor I. Bussel is a board-certified ophthalmologist and fellowship-trained surgeon affiliated with the University of California, Irvine (UCI), the Gavin Herbert Eye Institute, and the UCI School of Medicine.

Last Updated: 2025-01-05

Sources & Guidelines

Medically Reviewed

Evidence-Based

Updated 2025-01-05

Related Calculators

mg/kg Calculator

Calculate medication dosage based on body weight using the mg/kg formula. Essential for weight-based dosing in pediatric and adult medicine.

General Dose Math

mg ↔ mL Calculator

Convert between milligrams (mg) and milliliters (mL) using medication concentration. Essential for liquid medication dosing.

General Dose Math

Amoxicillin 400mg/5mL

Calculate the correct mL dose of amoxicillin 400mg/5mL suspension for children based on weight. Includes standard and high-dose options.

Pediatric

Gabapentin for Dogs

Calculate the correct gabapentin dose for your dog based on weight. Includes dosing for pain, anxiety, and seizures with dosage chart.

Veterinary+ Chart

References

Reviewed by: Clinical Review Team (RN, BSN)

Last updated: 2025-01-05