Dosage Calculation Formula Sheet (Free, Printable)

One page to print: dimensional analysis in 5 steps, ratio and proportion, the metric conversion table, and the rounding rules that decide whether a computed number counts as right. Below the sheet are 6 drill problems and a full answer key, all with invented numbers. Ctrl+P (Cmd+P on Mac) prints the sheet and the problems; the sheet section fits a single page.

How to use this page: print the sheet, tape it where you study, and run one problem a day against it until the setup happens without looking. Then work the 6 problems on paper and grade yourself with the answer key at the bottom. Prefer working from questions first? The free dosage calculations practice page gives you 8 problems with answers worked inline instead.

The formula sheet

Metric conversion table

ConvertMultiply byExample
kg → g× 1,0000.5 kg = 500 g
g → mg× 1,0000.25 g = 250 mg
mg → mcg× 1,0000.5 mg = 500 mcg
L → mL× 1,0001.2 L = 1,200 mL
lb → kg÷ 2.244 lb = 20 kg
tsp → mL× 51.5 tsp = 7.5 mL
oz → mL× 304 oz = 120 mL

Dimensional analysis in 5 steps

  1. Write the unit of the answer first. "tablets" or "mL/hr" goes at the far left before any math starts.
  2. Start with the given quantity as a fraction. The number the problem hands you, written with its unit, over 1.
  3. Chain conversion factors so unwanted units cancel diagonally. Keep each factor as a fraction and cancel until only the answer's unit survives.
  4. Multiply the numerators, divide by the denominators. One arithmetic pass, no intermediate rounding.
  5. Check the unit, then check the size. The surviving unit must match step 1, and the answer must pass the sanity check below.

given × (conversion 1) × (conversion 2) ... = answer with the unit from step 1

Ratio and proportion (mini version)

known : quantity :: desired : X   ⇒   known × X = desired × quantity  ⇒  X = (desired × quantity) ÷ known

Arithmetic example with invented numbers: stock strength 250 mg per tablet, amount to account for 750 mg.

250 mg : 1 tablet :: 750 mg : X  ⇒  250X = 750  ⇒  X = 3 tablets  ⇒  3 tablets of 250 mg = 750 mg

Formula method shortcut: desired ÷ have × quantity = 750 ÷ 250 × 1 = 3 tablets. Same result, one line.

Rounding and sanity checks

Typical rounding conventions: tablets to the nearest half or whole (capsules never split), drops (gtt) to whole drops, mL/hr pump rates to one decimal, liquid doses to two decimals or the nearest 0.25 mL syringe mark. Your program's policy overrides everything here.

Size sanity check: an answer of 12 tablets, 3 full liters, or 150 gtt/min usually means a decimal or a unit died somewhere in step 3. Redo the setup, not the arithmetic.

6 practice problems

All numbers are invented for drill. Work each on paper with units written at every step before you look at the answer key below.

  1. Problem 1 (conversion). A drill order reads 0.5 mg of a fictional substance. The stock card reads 250 mcg per tablet. How many tablets does the arithmetic call for?
  2. Problem 2 (liquid). A drill order reads 50 mg of a fictional substance. The stock strength is 20 mg per 5 mL. How many mL does the arithmetic call for?
  3. Problem 3 (weight-based). A drill order reads 15 mg per kg per day, divided into 2 equal doses. The figure on the problem sheet is 44 lb. The stock strength is 100 mg per 2 mL. How many mL does each dose call for?
  4. Problem 4 (pump rate). A drill bag holds 1,000 mL and must run over 8 hours. What pump rate in mL/hr does the arithmetic call for?
  5. Problem 5 (drip rate). A drill bag holds 500 mL and must run over 4 hours on tubing rated 20 gtt/mL. What drip rate in gtt/min does the arithmetic call for?
  6. Problem 6 (infusion time). A pump runs at 125 mL/hr. How many hours does it take for 750 mL to run?

Answer key

1. Two tablets. Convert first: 0.5 mg × 1,000 = 500 mcg. Then desired ÷ have = 500 ÷ 250 = 2 tablets. Check: 2 tablets of 250 mcg = 500 mcg = 0.5 mg.

2. 12.5 mL. Concentration: 20 mg per 5 mL. Desired ÷ have × quantity = 50 ÷ 20 × 5 = 12.5 mL. Check: 12.5 mL is 2.5 five-mL portions, and 2.5 × 20 mg = 50 mg.

3. 3 mL per dose. Weight: 44 lb ÷ 2.2 = 20 kg. Daily amount: 15 × 20 = 300 mg per day. Per dose: 300 ÷ 2 = 150 mg. Volume: 150 ÷ 100 × 2 = 3 mL. Check: two doses of 3 mL = 6 mL, and 6 mL at 50 mg/mL carries 300 mg, matching the daily figure.

4. 125 mL/hr. Rate = total volume ÷ hours = 1,000 ÷ 8 = 125 mL/hr. Check: 125 × 8 = 1,000 mL, matching the bag.

5. 42 gtt/min. Minutes: 4 hr × 60 = 240 min. Drip rate = (500 × 20) ÷ 240 = 10,000 ÷ 240 = 41.67. Drops count in whole numbers, so round to 42 gtt/min.

6. 6 hours. Time = volume ÷ rate = 750 ÷ 125 = 6 hours. Check: 125 × 6 = 750 mL, matching the amount.

5 mistakes that cost the most points

These are opinions from watching people drill this material, not survey data, but each one has a specific fix you can practice.

  1. Converting after the math instead of before. If the order reads mg and the stock card reads mcg and you divide anyway, the answer is wrong by a factor of 1,000 no matter how careful the division was. Match the units at setup, when the fix costs seconds.
  2. Treating per-dose and per-day figures as interchangeable. A problem written as "mg per kg per day, divided into 3 doses" has three different numbers in it. Label each step with its full unit (mg/day, mg/dose) and the swap stops happening.
  3. Trusting the calculator over the units. A calculator returns a number; only the setup decides what that number means. If the units do not cancel to the answer's unit, the number is garbage regardless of how clean it looks.
  4. Skipping the size check. Most programs build in the expectation that you notice an answer of 12 tablets before submitting. Ten seconds of "is this plausible?" catches the decimal slips that pure re-checking misses.
  5. Rounding in the middle of the chain. Rounding 41.67 to 42 mid-calculation, then multiplying by something else, compounds the error. Round once, at the end, using the rule that applies to that answer type.

Frequently asked

What is the fastest dosage calculation method? Whichever one you can run without hesitating. The formula method solves simple tablet and liquid problems in one line. Dimensional analysis chains the conversions into the setup itself, so multi-step problems stop feeling like separate steps. Most people settle on dimensional analysis for anything with two or more conversions and the formula method for the rest. Pick one for the whole practice session so the setup becomes automatic.

How do I memorize metric conversions? Memorize one number instead of a table: each step between kilo, base, milli, and micro is 1,000. The oddballs are worth writing on the sheet: pounds to kilograms is divide by 2.2, teaspoon to milliliters is 5, and ounce to milliliters is 30. Print the table above and work five conversion drills; by the fifth one you will stop looking at it.

Get the full 150-problem workbook →

one-time · 150 problems with worked step-by-step solutions · conversions, oral, liquids, weight-based, IV rates, infusion times · printable drills + answer keys

Study aid only - always verify with your program's references. All numbers on this page are invented for arithmetic drill, and the rounding conventions shown are common defaults, not any specific program's policy. This page is not medical advice and does not cover any real substance or protocol.