mg/kg Dosage Calculator
One dose
– mg
Enter the order and a body weight.
- Daily total
- –
- Volume per dose
- –
The working
This works out the arithmetic. The order, the product in your hand and local policy still govern what is given.
How to calculate a weight-based dose
dose in mg = mg/kg × weight in kg
That is the whole arithmetic. What makes weight-based dosing error-prone is not the multiplication but the two things that have to be established before it: which weight, and whether the figure is per dose or per day.
Per dose and per day are not the same order
Take 30 mg/kg for a 20 kg child, given three times a day, and read it both ways:
| How the order reads | One dose | Daily total |
|---|---|---|
| 30 mg/kg/day in three divided doses | 200 mg | 600 mg |
| 30 mg/kg per dose, three times a day | 600 mg | 1800 mg |
Same drug, same child, same frequency, and a threefold difference in everything given. This is why the calculator prints both totals on every result rather than only the one you asked for.
Pounds, kilograms and the weight to dose on
Weight-based dosing runs on kilograms. A weight recorded in pounds is divided by 2.2046 first, and dosing on the pound figure by mistake more than doubles the dose. The calculator converts and shows the step.
Which weight to use is a separate question again. Most paediatric dosing uses current actual weight. Some adult drugs specify ideal or adjusted body weight, which theideal body weight calculator works out, and cytotoxics are usually written in mg/m² against body surface area instead of weight at all.
Once the dose in milligrams exists, turning it into a measurable volume is themg to mL conversion, which this page will run for you if you fill in the strength.
Questions about weight-based dosing
- How do I calculate a mg/kg dose?
- Multiply the mg/kg figure by the body weight in kilograms. The result is a single dose if the order is written per dose, or a daily total if it is written per day, in which case divide by the number of doses to get one dose.
- What is the difference between mg/kg and mg/kg/day?
- mg/kg is usually a single dose. mg/kg/day is the total across the whole day, which then gets divided by the number of doses. An order of 30 mg/kg/day in three doses gives a third of what 30 mg/kg per dose three times a day would give.
- How do I convert pounds to kilograms for dosing?
- Divide by 2.2046, or multiply by 0.4536. A common error is dosing on the pound figure directly, which more than doubles the dose, so the weight unit is worth checking before anything is multiplied.
- What happens when a weight-based dose exceeds the adult maximum?
- Many paediatric orders reach the adult maximum in a larger child, at which point the maximum applies rather than the weight-based figure. This calculator compares the two and flags when the calculated dose is above the maximum you enter, rather than capping it silently.