Medication Dosage Calculator
This medication dosage calculator turns a prescribed dose into the exact millilitres to draw from a liquid. Enter the dose and the concentration on the bottle, or switch to weight-based mode to give a mg per kilogram order and a patient weight. It reads labels like 250 mg per 5 mL, converts pounds to kilograms, and shows the formula so you can check every step.
- mL to draw
- Weight-based mg/kg
- Reads mg per 5 mL
- Pounds or kilograms
- Doses per bottle
Last updated July 20, 2026 Standard dose-to-volume arithmetic Reviewed by the Calcowa team
That is 50 mg per mL. A label of 250 mg per 5 mL means 50 mg in every millilitre.
Optional: bottle size for doses per bottle
90 mg from a 50 mg per mL liquid.
A guide only. Confirm every dose with the prescription and a pharmacist before giving it.
Reading a concentration label as mg per mL
Liquid medicines print the strength per a set volume, not per single millilitre, so the first step is always to convert. Divide the strength by the volume to get mg per mL, then divide the ordered dose by that number. These are common label formats and the mg per mL they work out to, using plain arithmetic.
| Label on the bottle | Works out to | mL for a 100 mg dose |
|---|---|---|
| 125 mg / 5 mL | 25 mg/mL | 4 mL |
| 200 mg / 5 mL | 40 mg/mL | 2.5 mL |
| 250 mg / 5 mL | 50 mg/mL | 2 mL |
| 400 mg / 5 mL | 80 mg/mL | 1.25 mL |
| 500 mg / 5 mL | 100 mg/mL | 1 mL |
| 100 mg / 1 mL | 100 mg/mL | 1 mL |
| 20 mg / 1 mL | 20 mg/mL | 5 mL |
The strengths above are label formats for the math, not a recommendation to use any particular product or dose.
How the dosage math works
Every liquid dose is one division: the dose you need divided by how concentrated the liquid is. The concentration itself is the strength on the label divided by its volume. For a weight-based order you add one step first, multiplying the mg per kilogram by the patient weight to get the total dose, then divide as before.
The doctor orders 5 mg/kg, the child weighs 18 kg, and the bottle reads 250 mg per 5 mL. First the total dose: 5 × 18 = 90 mg. Next the concentration: 250 ÷ 5 = 50 mg/mL. Finally the volume: 90 ÷ 50 = 1.8 mL to draw. If the same bottle were 125 mg per 5 mL instead, that is 25 mg/mL, so the volume would double to 3.6 mL, which is why the exact label matters.
Frequently asked questions
You divide the dose you need by the concentration of the liquid. If the order is 90 mg and the bottle is 50 mg per mL, then 90 divided by 50 is 1.8 mL to draw. The only trick is reading the label correctly: a strength like 250 mg per 5 mL is really 50 mg per mL, so convert the label to mg per mL first, then divide the dose by that number. This medication dosage calculator does both steps for you and shows the working so you can check it by hand.
Many medicines, especially for children, are ordered per kilogram of body weight. You multiply the dose per kilogram by the patient's weight in kilograms to get the total dose, then convert that dose to a volume using the concentration. For a 5 mg/kg order and an 18 kg child, the total is 90 mg; from a 250 mg per 5 mL bottle that is 1.8 mL. Switch this tool to weight-based mode and it multiplies and divides in one step. Always confirm the mg/kg figure against the prescription, not from memory.
That label means every 5 mL of liquid contains 250 mg of the active ingredient. To get the concentration per single mL, divide the strength by the volume: 250 divided by 5 is 50 mg per mL. Working in mg per mL makes the dose math simple, because you just divide the ordered dose by that one number. Enter the two label figures in the concentration boxes here and the tool shows the mg per mL for you.
Yes. Pick pounds as the weight unit and the tool converts to kilograms before it applies the mg/kg dose, since clinical dosing is defined per kilogram. One pound is about 0.4536 kilograms, so a 40 lb child is roughly 18.1 kg. Because a small rounding difference in weight can shift the final dose, weigh the patient rather than estimating when the dose matters.
Open the optional bottle size box and enter the total volume of the container in mL. The tool divides the bottle volume by the volume of one dose to estimate how many full doses it holds, and shows the total milligrams in the bottle. Treat that as a rough guide for planning refills, not an exact count, because the last partial dose and any priming loss are not included.
No. It is an educational estimate that does the arithmetic, not a clinical tool and not a substitute for a professional. It cannot know the right drug, the right dose, a safe maximum, interactions, or a patient's kidney or liver function. Dosing errors can cause serious harm. Always follow the prescription and the pharmacy label, and confirm any dose with a licensed doctor, nurse, or pharmacist before giving it.
Usually because the concentration entered does not match the exact product. The same drug comes in several strengths, and a suspension can be 125 mg per 5 mL or 250 mg per 5 mL, which changes the volume by half. Check the concentration printed on your bottle and enter those exact numbers. If the pharmacy's directions still differ from the math, follow the pharmacy and ask them to explain, because they are dosing for the specific product and patient.
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Double-check before you draw
Match the concentration to your exact bottle, then confirm the dose with a pharmacist.