Free med-math tool
Nursing dosage calculator
Work oral and parenteral doses, IV flow rates in mL/hr, IV drip rates in gtt/min, and weight-based mg/kg dosing — and see the dimensional-analysis setup behind every answer, not just the number. Free, no signup, and it runs in your browser.
Interactive calculator
Dosage & med-math calculator
Pick a mode, enter the numbers from the order, and read the worked setup below the result — the same dimensional-analysis steps you show on an exam. Results update as you type.
For tablets, capsules, or a liquid, enter what the provider ordered (Desired), the strength you have on hand (Have), and the amount that strength comes in (Quantity — e.g. 1 tablet or 5 mL).
Result
Enter the values above to see the answer and the worked setup.
For education and practice only. This tool is a study aid, not a substitute for clinical judgment, a drug reference, or institutional policy. Always independently verify a dose — and use required double-checks for high-alert medications — before administering anything to a patient.
How it works
One method, four formulas
Every mode uses dimensional analysis: arrange the numbers so the units you do not want cancel and the unit you need is left. Learn the setup once and an unfamiliar problem stops being a guess.
Oral & parenteral dose
Amount to give = (Desired ÷ Have) × Quantity
The workhorse formula for tablets, capsules, and liquids. Put Desired (what was ordered) and Have (the strength on hand) into the same unit, divide, then multiply by the quantity that strength comes in.
IV flow rate
Rate (mL/hr) = Volume (mL) ÷ Time (hr)
Programs a volumetric pump. If the order gives the time in minutes, convert to hours first. Modern pumps are set in milliliters per hour, so this is the everyday IV calculation.
IV drip rate
gtt/min = (Volume × drop factor) ÷ Time (min)
For gravity tubing counted by drops. The drop factor (gtt/mL) is printed on the tubing package — 10, 15, or 20 for macrodrip, 60 for microdrip. Drops are whole, so the answer is rounded to a whole number.
Weight-based dose
kg = lb ÷ 2.2, then dose = kg × mg/kg/day ÷ doses
Common for pediatric and high-alert drugs. Convert the weight to kilograms first, multiply by the ordered mg per kg per day, then divide by the number of daily doses to get each dose.
Worked example
An IV drip rate, step by step
The order
Infuse 1,000 mL of a solution over 8 hours using gravity tubing with a drop factor of 15 gtt/mL. What is the drip rate in gtt/min?
The setup
- 1. Time to minutes: 8 hr × 60 = 480 min.
- 2. gtt/min = (1,000 mL × 15 gtt/mL) ÷ 480 min.
- 3. = 15,000 ÷ 480 = 31.25 gtt/min.
- 4. Round to whole drops → 31 gtt/min.
Answer: 31 gtt/min.
Why it works
The drop factor converts milliliters into drops, and dividing by the total minutes spreads those drops evenly across the infusion. The units cancel cleanly: mL × (gtt/mL) leaves gtt, and dividing by minutes gives gtt/min.
Because you can only count whole drops, 31.25 rounds to 31 gtt/min — round only at this final step. Enter the same numbers in the Drip mode above and you will see this exact worked setup returned.
Tip: with microdrip tubing (60 gtt/mL) the gtt/min always equals the mL/hr rate, which is a fast sanity check.
Common questions
Dosage calculation, explained
- How do I calculate a medication dose?
- Use the formula Amount to give = (Desired ÷ Have) × Quantity. Convert the ordered dose (Desired) and the strength you have on hand (Have) into the same unit first, divide, then multiply by the quantity that strength comes in — 1 tablet, or the milliliters a liquid strength is measured in. The calculator does the conversion and shows each step.
- How do I calculate IV drip rate in gtt/min?
- Multiply the volume in milliliters by the tubing's drop factor in gtt/mL, then divide by the time in minutes: gtt/min = (mL × drop factor) ÷ minutes. The drop factor is printed on the tubing package. Because you count whole drops, round the answer to a whole number.
- What is a drop factor and where do I find it?
- The drop factor is the number of drops per milliliter a particular IV tubing set delivers, and it is printed on the tubing package. Macrodrip sets are typically 10, 15, or 20 gtt/mL; microdrip (pediatric) tubing is 60 gtt/mL. With 60 gtt/mL tubing, the gtt/min rate equals the mL/hr rate.
- How do I convert pounds to kilograms for weight-based dosing?
- Divide the weight in pounds by 2.2 to get kilograms (1 kg = 2.2 lb). Always convert to kilograms before multiplying by a mg/kg dose — mixing up pounds and kilograms is one of the most common and dangerous med-math errors.
- When should I round, and to what?
- Keep full precision through the work and round only at the final step. Drops per minute are always whole numbers; IV pump rates are usually whole mL/hr (some smart pumps accept tenths); and you cannot split an unscored solid tablet. Follow the rule the problem or your institution states.
- Is this dosage calculator free, and can I use it on my phone?
- Yes. The calculator is completely free, needs no account, and runs entirely in your browser, so it works on a phone. It is a study and practice aid only — always verify any real dose against the order, the drug reference, and institutional policy before administering.
Turn the method into a reflex
Study the method, then drill the problems
The calculator does the arithmetic; getting fast and safe takes repetition with feedback. Read the dosage study guide for the full method and rounding rules, then practice fill-in dosage problems with worked solutions — or sit a full mixed practice exam.
This calculator and all study material on this site are provided for practice and study only — they are not medical advice or a substitute for clinical judgment, a drug reference, or institutional policy. Verify every dose before administering. NCLEX® is a registered trademark of the National Council of State Boards of Nursing, Inc. (NCSBN), which does not endorse or sponsor this site.