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. 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
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.
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.
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.
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.
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.
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. Verify every dose before administering.
More free tools
Related calculators
Reach for these alongside this one — the calculations that most often come up together on the wards and in practice questions.
IV Drip Rate Calculator
Convert an ordered volume and time into gtt/min or mL/hr for any drop factor.
Heparin Drip Rate Calculator
Weight-based heparin infusion rates and bolus volumes from the bag concentration.
Pediatric Safe Dose Calculator
Check an ordered pediatric dose against the safe mg/kg range and daily maximum.
Practice these — free questions
Apply it on real NCLEX-style questions
A calculator hands you the number; the exam makes you reach it under pressure and defend it. Drill Dosage Calculations questions that put this calculation inside a realistic clinical scenario — each one with a written rationale, so you learn why the answer is right, not just what it is. That explained-rationale practice is what sets us apart from a bare calculator.
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