Nessa, RN - February 14, 2022

# Dosage Calculations Made Easy for Nursing Students

Whether you're pre-nursing, currently a nursing student, or new nurse, understanding how to calculate drug dosages is a vital concept to master.
Medication administration is a core competency for all nurses in any clinical setting. Accurately calculating dosages is a crucial skill required to safely administer medications. While there is technology to help prevent medication errors i.e.  bar code scanning and smart infusion pumps, we cannot fully rely on these advancements.  The simplest calculation strategy we'll go over today is the universal formula, also known as the "desired over have" method. Want the full study step-by-step dosage calculation guide? Don't forget to get yours today for 50% off!

## Universal Formula: Desired Over Have Method

Desired over have = the desired amount (D) aka the dose prescribed and the amount on hand (H) or the amount you “have” available. The quantity (Q) is the form and amount in which the drug is supplied (i.e. tablet, capsule, liquid). To calculate the dose, take the desired amount and divide it by the amount on hand, then multiply it by the quantity, like this:

Example 1: Administer 250 mg of xyz med. You have xyz med in 500 mg tablets. How many tablets are you going to give?
Dose: 250 mg
Have: 500 mg
Quantity: 1 tablet
200 ÷ 500 x 1 = 0.5
Write final answer correctly: 0.5 tablets (NOT 0.50)

### IV Infusion: What is the rate (mL/hr)? How many hours? How much to infuse (mL)?

What if you're asked to infuse a medication over LESS than 1 hour, such as 15 minutes, 30 minutes, or 45 minutes?
15 minutes: this is 1/4 of an hour, so 0.25 hours.
30 minutes: this is 1/2 of an hour, so 0.50 hours.
45 minutes: this is 3/4 of an hour, so 0.75 hours.
Simply divide the minutes by 60 as shown in the table below. Remember, you need to administer the milliliters per hour, so we have to have our time in hours!

Example 1: Infuse LR 500 ml over 4 hours. What is the rate?
500 ml ÷ 4 hours = 125 ml/hr

Example 2: Infuse NS 300 ml over 30 minutes. What is the rate?
300 ml ÷ 0.5 hours = 600 ml/hr

Example 3: Infuse 1 liter over 5 hours. What is the rate?
Remember we need to convert liter → ml first (add 3 zeros: 1 liter = 1,000 ml)
1,000 ml ÷ 5 hours = 200 ml/hr

### Infusion Completion Times

Example 1: An IV medication was started at 0615 and will take 6 hours to infuse. What time will it be completed? Answer in military time.
1. Add 6 hours to 0615 (6:15am)
2. 6 hours from 0615 is 1215
3. Answer in military time: 1215

Example 2: You started an IV infusion of 1,000 ml NS on Monday at 1600. If the infusion rate is 100 ml/hr, what day and time will it be completed? Answer in military time.
Formula: Volume (ml) ÷ infusion rate (ml/hr) = hours to complete
1. 1,000 ml ÷ 100 ml/hr = 10 hours
2. Add 10 hours to Monday 1600 (4pm)
3. That gives us 0200 (2am) on Tuesday
4. Answer in military time: Tuesday 0200

### Ultimate Dosage Calculation Study Guide

Nursing school is hard enough, this is why I created a dosage calculation nursing study guide bundle for you! My dosage calculation study guide includes step-by-step calculations and examples from this post along with how to calculate IV drip rate (gtt/min), weight-based calculations and reconstitution medications. Get your complete 5-page dosage calculation study guide bundle today for 50% off before the sale ends!

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### Dosage Calculations Nursing Study Guide Bundle

\$2.99
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Dosage Calculations Nursing Cheat Sheets Bundle (5 pages)

Drug dosage calculations for nurses is a core competency for all nurses in every clinical setting. A key skill required to safely dispense drugs is the ability to perform accurate dosage calculations.

This nursing study guide bundle is designed to help you become competent in making drug calculations and can also be used as a reference guide. The guide is minimalistic and easy-to-understand with step-by-step examples so that it is less daunting. This is a must-have for pharmacology or nursing school in general!

Dosage Calculations Nursing Study Guide Bundle includes:

• Step-by-step formulas (no complicated dimensional analysis!)
• Examples with step-by-step solutions
• Examples include drug labels
• Reference sheet with drug calculation formulas & most common conversions

For Personal Use Only: Sharing, distributing, and reselling is prohibited

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LEGAL DISCLAIMER: The information contained on this website and this study guide are intended for educational purposes only. The content on this website is intended to guide nursing practice and does not supersede any individual healthcare provider’s scope of practice or any nursing school curriculum. Additionally, no content on this website is intended to be a substitute for professional medical advice, diagnosis or treatment.

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