Dose Calculator (mg to mL)

Liquid Dosage Calculations Explained

Administering the correct amount of liquid medication is critical in nursing, pharmacy, and home care. The most common method used to calculate the volume needed is the **"Desired Over Have"** formula.

The Formula

( Desired Dose / Have Dose ) × Quantity = Amount

• Desired (D): The amount prescribed by the doctor (e.g., 500 mg).
• Have (H): The strength of the medication available or on hand (e.g., 250 mg).
• Quantity (Q): The volume that contains the "Have" strength (e.g., 5 mL).

Example Calculation

Prescription: Amoxicillin 400 mg PO.

Available: Bottle label reads "250 mg per 5 mL".

1. D = 400 mg
2. H = 250 mg
3. Q = 5 mL
4. Calculation: (400 ÷ 250) × 5
5. Step 1: 400 ÷ 250 = 1.6
6. Step 2: 1.6 × 5 = 8 mL

Safety Tips

1. Double Check Units: Ensure the Desired and Have doses are in the SAME units (e.g., both mg or both mcg). If one is in grams and the other in mg, convert them first.

2. Measure Correctly: Use an oral syringe or a calibrated medicine cup. Kitchen spoons are NOT accurate.

3. Meniscus Rule: When measuring in a cup, read the liquid level at the bottom of the curve (meniscus) at eye level.