Dosage Calculations Calculator

Medical Dosage Calculator

Quickly calculate medication administration amounts using the "Desired Over Have" formula.

The amount of medication the doctor has ordered (e.g., mg, mcg, units).

The strength available on the label (e.g., 250 mg per tablet/5mL).

The quantity the dose comes in (e.g., 1 tablet, 5 mL, 1 capsule).

Amount to Administer:

function calculateDosage() { var desired = parseFloat(document.getElementById('desiredDose').value); var hand = parseFloat(document.getElementById('doseOnHand').value); var qty = parseFloat(document.getElementById('quantity').value); var resultDiv = document.getElementById('dosageResult'); var finalDisplay = document.getElementById('finalAmount'); if (isNaN(desired) || isNaN(hand) || isNaN(qty) || hand <= 0) { alert('Please enter valid positive numbers. Dose on Hand cannot be zero.'); resultDiv.style.display = 'none'; return; } var dosage = (desired / hand) * qty; // Format to max 3 decimal places var formattedDosage = Math.round(dosage * 1000) / 1000; finalDisplay.innerText = formattedDosage; resultDiv.style.display = 'block'; }

Understanding Medication Dosage Calculations

In clinical practice, ensuring medication safety is paramount. One of the most common methods used by healthcare professionals for pharmaceutical math is the "Desired Over Have" formula. This calculator automates that process to help verify manual calculations and prevent medication errors.

The Standard Formula

The calculation uses the following universal ratio:

(Dose Ordered / Dose on Hand) × Quantity = Amount to Administer

Key Components Explained

• Desired Dose (D): This is the specific dose of medication prescribed by the healthcare provider (e.g., 500mg).
• Dose on Hand (H): This is the dosage strength available on the medication label (e.g., 250mg).
• Quantity (Q): Also known as the vehicle or volume. This is the unit in which the "Have" dose is contained (e.g., 1 tablet, 5mL of liquid, or 1 vial).

Practical Examples

Example 1: Tablet Calculation
Order: Amoxicillin 500mg PO.
Available: 250mg per tablet.
Calculation: (500 / 250) × 1 tablet = 2 tablets.

Example 2: Liquid Medication
Order: Acetaminophen 650mg PO.
Available: 160mg per 5mL.
Calculation: (650 / 160) × 5mL = 20.31 mL.

Important Safety Reminders

While this calculator is a helpful tool, clinical judgment should always come first. Always consider the following:

1. Unit Consistency: Ensure both the "Desired Dose" and "Dose on Hand" are in the same units (e.g., both in mg or both in mcg). If they are different, convert them before calculating.
2. The Five Rights: Always verify the Right Patient, Right Drug, Right Dose, Right Route, and Right Time.
3. Double Check: For high-alert medications (like insulin or heparin), always have a second practitioner verify your calculation manually.
4. Decimal Places: Be cautious when rounding. Pediatric doses often require rounding to the nearest hundredth, whereas adult doses may be rounded to the tenth.

Disclaimer: This tool is for educational purposes only. All clinical calculations should be verified manually and checked against institutional protocols before medication administration.