Med Math Practice Quiz
True / False
True / False
True / False
True / False
Med Math Setup Traps: Units, Time, and Concentration Mix-ups
1) Mixing patient weight units (lb vs kg)
Most EMS protocols order mg/kg or mcg/kg/min. If weight is in pounds, convert first and then stop writing lb anywhere in the setup. Use kg = lb ÷ 2.2. A quick self-check is that adult weights in kg often fall between 40 and 120.
2) Blurring “dose ordered” with “dose on hand”
“Give 4 mg” is not the same as “4 mg/mL.” Keep two labeled lines: Desired dose (order) and Dose on hand (vial or syringe). Then apply the Master Formula with the actual label concentration and volume.
3) Prefix errors (mg vs mcg) and missing the 1,000 factor
Infusions often use mcg/kg/min while bags are mixed in mg. Write the prefix on every number and every intermediate result. Convert deliberately using 1 mg = 1,000 mcg. If your final rate changes by a factor of 1,000 after a “late” conversion, the setup was not controlled.
4) Dropping time units during infusions
Pumps require mL/hr, but many orders are per minute. Keep min and hr visible until the last step. Convert mcg/min to mcg/hr by multiplying by 60 before solving for mL/hr.
5) Using gtt/min without a drop factor
Gravity drip math is not solvable without tubing drop factor. Microdrip is 60 gtt/mL. Macrodrip is commonly 10, 15, or 20 gtt/mL. If it is not specified, flag the question as missing data.
6) Rounding too early
Carry at least two decimals through conversions and concentration steps. Round once at the end based on what you can measure or program (syringe markings, pump increment, whole drops for gtt/min).
EMS Med Math Master Formula + Infusion Conversion Quick Sheet (Printable)
Print/save as PDF: Use this as a one-page reference while practicing calculations.
Core workflow (use for every question)
- Write the goal unit first (mL, mg, mcg/min, mL/hr, gtt/min).
- Convert early (lb to kg, g to mg, mg to mcg, min to hr).
- Label every number with units and cross-cancel units line by line.
- Round once at the end, based on measurable or programmable increments.
- Run a reasonableness check: does the dose, volume, and rate fit clinical reality and the concentration provided?
High-use conversions
- kg = lb ÷ 2.2
- 1 g = 1,000 mg
- 1 mg = 1,000 mcg
- 1 hr = 60 min
Master Formula (volume to administer)
(Desired dose ÷ Dose on hand) × Volume on hand = Volume to give
- Desired dose: order or protocol dose (mg, mcg).
- Dose on hand: amount in vial, syringe, or vial strength (mg, mcg).
- Volume on hand: mL that contains the dose on hand.
Weight-based bolus dosing
- Total dose (mg or mcg) = ordered dose per kg × patient kg
- Then convert dose to mL using Master Formula or a given concentration (mg/mL, mcg/mL).
Concentration, dilution, and reconstitution
- Concentration = total drug amount ÷ final total volume
- Volume needed (mL) = ordered dose ÷ concentration
- For reconstitution, use the final volume (drug plus diluent), not the diluent alone.
Infusions
- Pump rate (mL/hr) = volume (mL) ÷ time (hr)
- Gravity drip (gtt/min) = (mL/hr × gtt/mL) ÷ 60
mcg/kg/min to mL/hr (common EMS pattern)
- Convert lb to kg.
- Compute mcg/min = (mcg/kg/min) × kg.
- Convert mcg/hr = mcg/min × 60.
- Compute bag concentration in mcg/mL.
- Solve mL/hr = mcg/hr ÷ (mcg/mL).
Step-by-Step Paramedic Med Math: mcg/kg/min to mL/hr and Bolus mL
Example 1: Infusion conversion (mcg/kg/min to mL/hr)
Order: 0.1 mcg/kg/min. Patient: 176 lb. Bag: 4 mg in 250 mL. Goal: mL/hr.
- Convert weight: 176 lb ÷ 2.2 = 80 kg.
- Compute mcg/min: 0.1 mcg/kg/min × 80 kg = 8 mcg/min.
- Convert to mcg/hr: 8 mcg/min × 60 = 480 mcg/hr.
- Find concentration: 4 mg = 4,000 mcg. 4,000 mcg ÷ 250 mL = 16 mcg/mL.
- Solve rate: 480 mcg/hr ÷ 16 mcg/mL = 30 mL/hr.
Reasonableness check: 30 mL/hr is a plausible pump rate and the units cancel cleanly to mL/hr.
Example 2: Master Formula for a bolus (mg to mL)
Order: 2 mg IV. Supply: 4 mg in 1 mL. Goal: mL to draw up.
- Desired dose = 2 mg.
- Dose on hand = 4 mg.
- Volume on hand = 1 mL.
- (2 mg ÷ 4 mg) × 1 mL = 0.5 mL.
Check: Half the mg equals half the volume because the concentration is linear.
Med Math Practice FAQ: Master Formula, Dimensional Analysis, and Pump Rates
Should I use the Master Formula or dimensional analysis for EMS med math?
Use either, but commit to one clean setup per question. The Master Formula is fast for “dose ordered” to “mL to give.” Dimensional analysis is safer for multi-step infusions because it forces units (mcg, kg, min, hr, mL) to cancel in a controlled way.
How do I prevent mg vs mcg infusion errors in mcg/kg/min problems?
Write the prefix on every line and convert the bag to a single concentration unit before solving. A reliable pattern is to convert the bag to mcg/mL first, then compute ordered mcg/hr, then divide to get mL/hr. If you see a factor-of-1,000 swing late in the work, restart and convert earlier.
What rounding is acceptable for paramedic pump rates and drip rates?
Round based on what you can deliver. For pump rates, follow the question’s pump increment if given, otherwise round to a practical decimal (often tenths). For gravity drips, you generally need a whole number of gtt/min, so round at the end after calculating with full precision.
What information must be present to calculate gtt/min?
You need the intended flow rate (usually mL/hr or total volume and time) and the tubing drop factor in gtt/mL. Microdrip is 60 gtt/mL. Macrodrip sets vary (often 10, 15, or 20 gtt/mL). If the drop factor is missing, the problem is incomplete.
I keep missing basic conversions. What else should I practice?
Practice conversions as short, timed drills: lb to kg, mg to mcg, and min to hr. If you want extra dosage calculation practice in a nursing testing format, use Nursing Entrance Exam Practice Test Questions for more unit-handling reps.
Looking for more? Browse more Healthcare & Medical quizzes on QuizWiz or explore the full QuizWiz workplace quiz library.