Med Math Practice

1) Core Conversions (Memorize)

If units don’t match, convert first.

2) Basic Dosage Formula (Most Common)

Formula:

(Dose Ordered ÷ Dose on Hand) × Quantity = Amount to Give

Example: Order 500 mg • On hand 250 mg tablets • Quantity 1 tab

(500 ÷ 250) × 1 = 2 tablets

3) Liquid Medications

Same formula — watch mL.

Example: Order 10 mg • On hand 20 mg / 5 mL

(10 ÷ 20) × 5 = 2.5 mL

4) IV Pump Rate (mL/hr)

Formula:

Total Volume (mL) ÷ Time (hr) = mL/hr

Example: 1000 mL over 8 hr

1000 ÷ 8 = 125 mL/hr

5) IV Drip Rate (gtt/min)

Formula:

(mL × drop factor) ÷ minutes = gtt/min

Example: 500 mL over 4 hr • Drop factor 15 gtt/mL

(500 × 15) ÷ 240 = 31 gtt/min

Round drops to a whole number.

6) Weight-Based Dosing (kg only)

Example: 22 lb child • Order 10 mg/kg

22 ÷ 2.2 = 10 kg
10 × 10 = 100 mg

7) Insulin Basics

Example: Order 15 units → draw up 15 units

8) Rounding Rules (Test Favorite)

If the question says “round to the nearest tenth,” do exactly that.

9) Dimensional Analysis (Unit-Cancel Method)

Write it top to bottom and cancel units as you go:

Ordered unit
────────────── × Quantity
On-hand unit

If units cancel correctly, you’re usually right.

10) Common Test Traps + Final Check

Traps:

Quick check before submitting:

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