Dosage Calculator: Tablets, Liquids, and Weight-Based Doses
Enter the dose ordered and the dose on hand to get the amount to give, with the formula and each step shown. The calculator covers tablets and capsules, liquids in mL, and weight-based doses in mg/kg, and converts between mcg, mg, and g and between pounds and kilograms.
- Both doses are in mg.
- 500 ÷ 250 = 2
- 2 × 1 = 2
How to calculate a dose
Most dosage problems use one formula: dose ordered ÷ dose on hand × quantity, where quantity is the tablet count or the liquid volume the dose on hand comes in. Put both doses in the same unit before dividing. For a liquid, the result is in mL.
A weight-based order gives a dose per kilogram. Convert the weight to kilograms (pounds ÷ 2.2), multiply by the dose per kilogram, and divide by the number of doses if the order is a daily total given in divided doses.
A calculator result is a check on the hand calculation. The order, the drug label, and facility policy decide what is given, and a pharmacist can confirm an unusual dose.
Common conversions
Dosage problems in nursing school and on the NCLEX use these equivalents.
| Unit | Equals |
|---|---|
| 1 gram (g) | 1,000 milligrams (mg) |
| 1 milligram (mg) | 1,000 micrograms (mcg) |
| 1 kilogram (kg) | 2.2 pounds (lb) |
| 1 liter (L) | 1,000 milliliters (mL) |
| 1 teaspoon (tsp) | 5 mL |
| 1 tablespoon (tbsp) | 15 mL |
| 1 fluid ounce (oz) | 30 mL |
Household measures (teaspoon, tablespoon, ounce) use the rounded equivalents taught in nursing dosage calculation; 1 kg is 2.2046 lb, rounded to 2.2.
Practice problems
Work each problem by hand, then open the answer to check it.
- The order is 750 mg. Tablets on hand are 250 mg. How many tablets?
Show answer
3 tablets. 750 mg ÷ 250 mg × 1 tablet = 3 tablets.
- The order is 0.5 g. Tablets on hand are 250 mg. How many tablets?
Show answer
2 tablets. Convert first: 0.5 g = 500 mg. Then 500 ÷ 250 × 1 = 2 tablets.
- The order is 200 mg of a suspension labeled 125 mg per 5 mL. How many mL?
Show answer
8 mL. 200 ÷ 125 × 5 mL = 8 mL.
- The order is 15 mg/kg for a child who weighs 33 lb. What is the dose?
Show answer
225 mg. 33 lb ÷ 2.2 = 15 kg. 15 mg/kg × 15 kg = 225 mg.
- The order is 40 mg/kg/day divided every 8 hours for a 20 kg child. What is each dose?
Show answer
266.67 mg. 40 × 20 = 800 mg a day. Every 8 hours is 3 doses: 800 ÷ 3 = 266.67 mg per dose.
Questions
- What is the formula for dosage calculation?
- Dose ordered divided by dose on hand, multiplied by the quantity the dose on hand comes in. With both doses in the same unit, the result is the number of tablets or the volume in mL to give.
- How do you convert pounds to kilograms for a dose?
- Divide the weight in pounds by 2.2. A 44 lb child weighs 20 kg, so a 10 mg/kg order is 200 mg.
- Is dosage calculation on the NCLEX?
- Yes. The NCLEX test plan lists "perform calculations needed for medication administration", and an on-screen calculator is provided during the exam.