Tools in This Collection
Medication Dosage Calculator
Calculate weight-based dosages and volumes for medication administration
IV Drip Rate Calculator
Convert medication orders to drops per minute or mL per hour
Medication Half-Life Calculator
Calculate drug concentration over time and elimination timeline
Drug Interaction Checker
Identify known interactions between common medications
Needle Gauge Chart
Match needle gauge to outer diameter, flow rate, and clinical use
AUDIT Alcohol Screening
WHO 10-question alcohol use disorders identification test
CAGE Alcohol Questionnaire
4-question bedside screen for alcohol use problems
These tools are for educational purposes and screening awareness — they do not replace professional medical evaluation. Always verify medication calculations with a licensed healthcare professional before administration.
Medication Calculation Workflow
Accurate medication calculations are foundational to safe clinical practice. These tools handle the math for common clinical calculations — weight-based dosing, infusion rates, drug elimination timelines, and alcohol use screening — reducing arithmetic errors in high-stakes situations.
Weight-Based Dosing
The Medication Dosage Calculator computes weight-based doses using the standard formula: dose (mg) = prescribed dose (mg/kg) × patient weight (kg). This is the primary method for pediatric dosing and for medications with narrow therapeutic windows in adults. For volume calculation: volume (mL) = dose (mg) ÷ concentration (mg/mL). A 25 kg child prescribed amoxicillin 40 mg/kg/day in three divided doses needs 333 mg per dose, or approximately 13 mL of a 250 mg/5 mL suspension per dose.
IV Infusion Rate Calculation
The IV Drip Rate Calculator converts medication orders to drops per minute (for manual infusion) or mL per hour (for electronic pumps). The formula for drops per minute: (volume in mL × drop factor) ÷ time in minutes. Standard drop factors: 10 gtt/mL (macrodrip), 15 gtt/mL (macrodrip), 60 gtt/mL (microdrip). For a 1,000 mL bag to infuse over 8 hours with a 15 gtt/mL set: (1000 × 15) ÷ 480 = 31 gtt/min.
Drug Elimination and Half-Life
The Medication Half-Life Calculator shows the drug concentration at any time point after the last dose. After one half-life, 50% remains; after two, 25%; after five half-lives, approximately 97% is eliminated — the practical definition of drug clearance. This is useful for understanding wash-out periods, timing of drug level tests, and estimating when a medication is no longer active.
Alcohol Screening
The AUDIT Alcohol Screening Tool is the WHO's 10-question Alcohol Use Disorders Identification Test. Scores of 8 or above suggest hazardous drinking patterns; 15+ indicate probable dependence. The brief CAGE Questionnaire (4 questions) is a quick bedside screen where 2 or more positive responses suggest an alcohol problem. The Drug Interaction Checker identifies known interactions between common medications. The Needle Gauge Chart provides quick reference for matching gauge numbers to outer diameter, flow rate, and clinical use cases.
Frequently Asked Questions
How do I calculate a weight-based medication dose?
Multiply the prescribed dose in mg/kg by the patient's weight in kg: dose (mg) = mg/kg × weight (kg). To find the volume to administer, divide the dose by the concentration: volume (mL) = dose (mg) ÷ concentration (mg/mL). For example: 10 mg/kg prescribed for a 30 kg child = 300 mg dose. If the medication is 50 mg/mL concentration: 300 ÷ 50 = 6 mL.
How do you calculate IV drip rate in drops per minute?
Use the formula: drops per minute = (volume in mL × drop factor) ÷ time in minutes. The drop factor is printed on the IV tubing package (typically 10, 15, or 60 gtt/mL). Example: 500 mL over 4 hours (240 minutes) with a 15 gtt/mL set = (500 × 15) ÷ 240 = 31 drops per minute. For electronic pumps, simply calculate mL/hr = volume ÷ hours.
What does medication half-life mean clinically?
Half-life is the time for drug concentration to decrease by 50%. After 5 half-lives, approximately 97% of the drug is eliminated — used as the practical definition of drug clearance. This determines dosing intervals: drugs with long half-lives (like fluoxetine at 1–4 days) dose less frequently; short half-life drugs (like ibuprofen at 2 hours) need more frequent dosing to maintain therapeutic levels.
What AUDIT score indicates a drinking problem?
AUDIT scores of 8–14 indicate hazardous or harmful alcohol use. Scores of 15 or above suggest probable alcohol dependence. The 10-question AUDIT takes about 2 minutes and is validated for primary care screening. Two or more positive responses on the 4-question CAGE questionnaire also suggest a clinically significant alcohol use problem warranting further evaluation.