Eight dosage calculation problems on this page: two conversions, two oral tablets, two weight-based doses, two IV rates. Every answer is worked step by step below its problem, with both the ratio method and the formula method where both apply. Ctrl+P (Cmd+P on Mac) prints the set for practice away from a screen. No sign-up, no email.
Metric conversions to memorize: 1 kg = 1,000 g · 1 g = 1,000 mg · 1 mg = 1,000 mcg · 1 L = 1,000 mL · 1 mL = 1 cc · 1 tsp = 5 mL · 1 tbsp = 15 mL · 1 oz = 30 mL
Formula method:
Ratio and proportion:
Weight-based dose: multiply the ordered mg/kg by the patient's weight in kg first, then treat the result as the desired dose.
IV rates: pump rate in mL/hr = total mL / hours. Gravity drip rate in gtt/min = (total mL × drop factor) / total minutes.
Rounding: tablets round to nearest half or whole tablet, drops (gtt) round to whole drops, pediatric doses to the hundredth, IV pump rates to one decimal place, unless your program's policy says otherwise.
Problem 1. The provider orders 0.5 mg of a medication. The unit-dose drawer stocks 500 mcg tablets. How many tablets do you give?
Answer: 1 tablet.
Step 1. Convert the order to the same unit as the stock. 1 mg = 1,000 mcg, so 0.5 mg × 1,000 = 500 mcg.
Step 2. Formula method: D/H × Q = 500 mcg / 500 mcg × 1 tablet = 1 tablet.
Ratio check: 500 mcg : 1 tab :: 500 mcg : X, so 500X = 500 and X = 1. The two units were identical after conversion, so one tablet is right.
Problem 2. A patient drank 4 oz of juice, 6 oz of coffee, and a full 240 mL cup of water. Record the total intake in mL.
Answer: 540 mL.
Step 1. Convert ounces to mL using 1 oz = 30 mL. Juice: 4 × 30 = 120 mL. Coffee: 6 × 30 = 180 mL.
Step 2. The water is already in mL: 240 mL.
Step 3. Add: 120 + 180 = 300 mL, and 300 + 240 = 540 mL.
Intake questions are conversion plus addition. Convert everything to mL before summing; mixing units mid-sum is the classic error. Quick check: 10 oz of drinks × 30 = 300 mL, plus the 240 mL water.
Problem 3. Order: 75 mg by mouth, once daily. Stock: 25 mg tablets. How many tablets per dose?
Answer: 3 tablets.
Formula method: D/H × Q = 75 mg / 25 mg × 1 tablet = 3 tablets.
Ratio method: 25 mg : 1 tab :: 75 mg : X ⇒ 25X = 75 ⇒ X = 3 tablets.
The units match already (mg to mg), so no conversion step. Three tablets, once daily.
Problem 4. Order: 0.375 mg by mouth now. Stock: 0.25 mg tablets. How many tablets do you give?
Answer: 1.5 tablets.
Formula method: D/H × Q = 0.375 mg / 0.25 mg × 1 tablet = 1.5 tablets.
Ratio method: 0.25 : 1 :: 0.375 : X ⇒ 0.25X = 0.375 ⇒ X = 1.5 tablets.
1.5 tablets is scoreable if the tablet is scored; if the stock is unscoreable, you would clarify with the prescriber. Decimal orders like 0.375 read best with the decimal moved to a fraction: 0.375 is 3/8 of a mg, and 0.25 is 1/4, so the ratio is 3/8 ÷ 1/4 = 3/2. Same answer, different check.
Problem 5. Order: a medication at 12 mg/kg/day divided into two doses. Patient weight: 44 lb. Stock: 60 mg tablets. How many tablets per dose?
Answer: 2 tablets (120 mg) per dose.
Step 1. Convert weight: 44 lb ÷ 2.2 = 20 kg.
Step 2. Total daily dose: 12 mg/kg × 20 kg = 240 mg/day.
Step 3. Divide by 2 doses: 240 ÷ 2 = 120 mg per dose.
Step 4. D/H × Q = 120 mg / 60 mg × 1 tab = 2 tablets per dose.
Check: 2 tablets × 2 doses = 240 mg/day, matching the daily order. Weight-based problems are three calculations in a row, so label each step (kg, mg/day, mg/dose) on paper; unlabeled steps are where the mg/day and mg/dose figures swap.
Problem 6. A child weighing 33 lb is ordered a medication at 10 mg/kg/dose, three times a day. Stock is an oral suspension of 100 mg per 5 mL. How many mL per dose?
Answer: 7.5 mL per dose.
Step 1. Convert weight: 33 lb ÷ 2.2 = 15 kg.
Step 2. Per-dose dose: 10 mg/kg × 15 kg = 150 mg per dose. The order says mg/kg/dose, so no division by three happens here; three times a day schedules the repeats, it does not shrink each dose.
Step 3. Suspension concentration: 100 mg per 5 mL. D/H × Q = 150 mg / 100 mg × 5 mL = 7.5 mL per dose.
Daily total, if asked: 150 mg × 3 = 450 mg/day, or 22.5 mL/day. Mixing up per-dose and per-day figures is the most common slip on weight-based problems, and mg/kg/dose versus mg/kg/day wording is what tells you which one the order wants.
Problem 7. An order reads 1,000 mL over 8 hours. The IV pump delivers in mL/hr. What rate do you set?
Answer: 125 mL/hr.
Setup: pump rate = total mL / hours = 1,000 mL / 8 hr = 125 mL/hr.
One division, no drop factor, because pumps meter volume per hour. Check: 125 mL/hr × 8 hr = 1,000 mL, which matches the order.
Problem 8. Order: 500 mL over 6 hours by gravity, tubing with a drop factor of 15 gtt/mL. What drip rate do you set?
Answer: 21 gtt/min.
Step 1. Total minutes: 6 hr × 60 = 360 min.
Step 2. gtt/min = (total mL × drop factor) / total minutes = (500 × 15) / 360 = 7,500 / 360 = 20.83...
Step 3. Drops count in whole drops, so round to 21 gtt/min.
Rounding to whole drops is standard because a drop either falls or does not. Check: 21 gtt/min × 360 min ÷ 15 gtt/mL = 504 mL, close to the 500 ordered, and the rounding accounts for the difference.
Which method should I use, ratio and proportion or the formula method? Pick one and use it for every problem so it becomes automatic. The formula method (desired over have times quantity) is fast for simple tablet and injection problems. Ratio and proportion handles the same problems and scales more cleanly to conversions and multi-step doses. The worked answers above show both.
How do I know if my answer is reasonable? Sanity-check the size. A tablet dose above 10 tablets, an adult weight-based dose above 100 mg per dose, or a drip rate above 100 gtt/min usually means a decimal moved. Rounding rules matter too: drops round to whole drops, tablets to halves or wholes, and IV pump rates to one decimal.
Get the full 150-problem workbook →one-time · 150 problems with worked step-by-step solutions · conversions, oral, injections, reconstitution, weight-based, pediatric, IV rates · printable drills + answer keys
Practice material only. Numbers here are invented for drill purposes and follow standard rounding conventions, not any specific institutional protocol. Verify every calculation against your program's or facility's policies before administration. This page is not medical advice.