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Simple Calculators

Nursing Dose Calculator

Calculate drug dosage volumes, weight-based doses (mg/kg), and IV drip rates using the Desired Over Have formula

Patient Information
Ordered Dose
Available Medication

e.g. 250 mg per 5 mL — enter the concentration as labelled on the vial/bottle

IV Drip Rate

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Quick summary

This nursing dose calculator uses the Desired Over Have formula to calculate how much volume to administer. It supports weight-based (mg/kg) dosing and calculates IV flow rates (mL/hr) and drip rates (gtts/min) for manual IV sets.

Reviewed by Simple Calculators TeamLast reviewed

For information only — not medical advice. Results are estimates from published formulas and can't account for your health history. Talk to a doctor or other qualified clinician before making health decisions.

How to use this calculator

  1. Enter the inputs requested by the calculator.
  2. Choose the units or options that match your situation and review the assumptions.
  3. Run or update the calculation to see the result.
  4. Review the result, breakdown, and formulas shown on the page.
  5. Check the inputs, units, dates, and limitations before saving or sharing the result.

Nursing Dose Formulas & Examples

Basic Dose Formula (Desired Over Have)

Volume=Desired DoseAvailable Strength×Available Volume\text{Volume} = \frac{\text{Desired Dose}}{\text{Available Strength}} \times \text{Available Volume}
Desired Dose
The dose ordered by the prescriber
Available Strength
The drug concentration on hand (e.g. 250 mg)
Available Volume
The volume that contains the available strength (e.g. 5 mL)

Worked example

Ordered 500 mg. Available: 250 mg per 5 mL.

Given
Desired = 500 mg
Have = 250 mg
Volume = 5 mL
Calculation
500250×5\frac{500}{250} \times 5
Result
10 mL to administer

Weight-Based Dosing

Total Dose=Dose per kg×Weight (kg)\text{Total Dose} = \text{Dose per kg} \times \text{Weight (kg)}
Dose per kg
Ordered dose in mg/kg (or mcg/kg)
Weight (kg)
Patient weight converted to kg

Worked example

5 mg/kg ordered for a 70 kg patient

Given
Dose per kg = 5 mg/kg
Weight = 70 kg
Calculation
5×705 \times 70
Result
350 mg total dose

IV Flow Rate

Flow Rate (mL/hr)=Total Volume (mL)Infusion Time (hr)\text{Flow Rate (mL/hr)} = \frac{\text{Total Volume (mL)}}{\text{Infusion Time (hr)}}
Total Volume
Total volume of IV fluid in mL
Infusion Time
Duration of infusion in hours

Worked example

100 mL to infuse over 60 minutes (1 hr)

Given
Volume = 100 mL
Time = 60 min
Calculation
1001\frac{100}{1}
Result
100 mL/hr

IV Drop Rate

gtts/min=Total Volume (mL)×Drop FactorInfusion Time (min)\text{gtts/min} = \frac{\text{Total Volume (mL)} \times \text{Drop Factor}}{\text{Infusion Time (min)}}
Drop Factor
Drops per mL (10, 15, 20, or 60 gtts/mL)
Infusion Time
Infusion time in minutes

Worked example

100 mL over 60 min with a 20 gtts/mL set

Given
Volume = 100 mL
Drop Factor = 20
Time = 60 min
Calculation
100×2060\frac{100 \times 20}{60}
Result
33.3 gtts/min

Frequently asked questions

What is the Desired Over Have formula?

The Desired Over Have formula is the standard method for calculating medication doses: Volume to administer = (Desired dose ÷ Available strength) × Available volume. It works for oral, IM, and IV medications.

How do I calculate a weight-based dose?

First calculate the total dose: Total dose = Dose per kg × Patient weight in kg. Then apply the Desired Over Have formula using the total dose. Example: 5 mg/kg for a 70 kg patient = 350 mg total.

What drop factors are commonly used?

Standard IV tubing is 20 gtts/mL or 15 gtts/mL. Macrodrip sets are 10–20 gtts/mL, microdrip (pediatric/precise) sets are 60 gtts/mL. Always check your tubing packaging.

How do I convert lbs to kg?

Divide pounds by 2.2046. For example, 154 lbs ÷ 2.2046 = 69.9 kg. This calculator does the conversion automatically when you select lbs.

Should I rely solely on this calculator for clinical decisions?

No. Always perform an independent double-check using a second method or colleague, follow your facility's medication administration protocols, and consult the prescriber for any uncertainty. This tool is a decision-support aid only.

Key terms

Desired Over Have
The standard nursing drug calculation formula: (Desired ÷ Have) × Volume = Volume to administer
Drop Factor (gtts/mL)
The number of drops per mL delivered by an IV administration set, printed on the tubing packaging
Weight-Based Dosing
Dosing based on patient body weight, commonly used for pediatric patients and certain drugs (e.g. mg/kg)
Flow Rate
The rate of IV infusion expressed in mL per hour (mL/hr), set on the IV pump
Drip Rate
The rate of manually-counted drops per minute (gtts/min) for gravity IV infusions without a pump

Methodology, sources & limitations

This page shows the formula, assumptions, and limitations used for this estimate. Rates, thresholds, and other time-sensitive inputs can change, so verify them against the relevant official source before relying on a result.

For our review approach and the primary sources we consult, see the methodology and source policy. If you spot an outdated figure or formula, please contact us with a correction.