Optional - HOSA Medical Math

Metric System

A decimal system of weights and measures based on the meter and the gram.

Household System

A system of measurement common in the United States using drops, teaspoons, and tablespoons.

Apothecary System

An older system of measurement using grains, drams, and minims (rarely used but tested).

Gram (g)

The basic unit of weight in the metric system.

Liter (L)

The basic unit of volume in the metric system.

Meter (m)

The basic unit of length in the metric system.

Milligram (mg)

One-thousandth ($1/1,000$) of a gram.

Microgram (mcg)

One-millionth ($1/1,000,000$) of a gram.

Kilogram (kg)

One thousand ($1,000$) grams.

Milliliter (mL)

One-thousandth ($1/1,000$) of a liter; equivalent to 1 cubic centimeter (cc).

1 kilogram

Equals 2.2 pounds (lb).

1 inch

Equals 2.54 centimeters (cm).

1 teaspoon (tsp)

Equals 5 milliliters (mL).

1 tablespoon (tbsp)

Equals 15 milliliters (mL).

1 ounce (oz)

Equals 30 milliliters (mL) or 30 grams (g).

1 cup

Equals 8 ounces (oz) or 240 milliliters (mL).

1 pint

Equals 16 ounces (oz) or 500 milliliters (mL).

1 quart

Equals 32 ounces (oz) or 1,000 milliliters (mL) or 1 liter (L).

1 grain (gr)

Equals 60 or 65 milligrams (mg) depending on the drug.

15 grains (gr)

Equals 1 gram (g).

Fahrenheit to Celsius

$C = (F - 32) \div 1.8$

Celsius to Fahrenheit

$F = (C \times 1.8) + 32$

Freezing point of water

0°C or 32°F.

Boiling point of water

100°C or 212°F.

Normal body temperature

37°C or 98.6°F.

Military Time

A 24-hour clock used to avoid AM/PM confusion.

0000 or 2400

Midnight in military time.

1200

Noon in military time.

1800

6:00 PM in military time.

0015

12:15 AM in military time.

Roman Numeral I

1

Roman Numeral V

5

Roman Numeral X

10

Roman Numeral L

50

Roman Numeral C

100

Roman Numeral D

500

Roman Numeral M

1000

Roman Numeral IV

4

Roman Numeral IX

9

Roman Numeral XL

40

Roman Numeral XC

90

Ratio

A relationship between two numbers (e.g., 1:10).

Proportion

An equation stating that two ratios are equal (e.g., 1:2 = 2:4).

Means

The inner numbers in a proportion.

Extremes

The outer numbers in a proportion.

Solving for X

In a proportion, the product of the means equals the product of the extremes.

Intake and Output (I&O)

The measurement of all fluids a patient takes in and eliminates.

Positive Fluid Balance

When intake is greater than output.

Negative Fluid Balance

When output is greater than intake.

1 mL

Equals 1 cc (cubic centimeter).

60 mg

Standard conversion for 1 grain (gr).

Micro-drip tubing

Delivers 60 drops (gtts) per mL.

Macro-drip tubing

Delivers 10, 15, or 20 drops (gtts) per mL.

Gtts

Abbreviation for drops.

Flow rate formula

$(V \div T) \times C = R$ (Volume/Time in mins x Drop Factor).

IV Infusion Time

$V \div R = T$ (Total Volume / Rate per hour).

Dosage on Hand

The amount of drug available in a specific unit (e.g., 250 mg per tablet).

Desired Dose

The amount of drug ordered by the physician.

Vehicle

The form in which a drug is available (e.g., tablet, liquid).

Dosage Formula

$(D \div H) \times Q = X$ (Desired / Have x Quantity).

BMI Formula (Metric)

$kg \div m^2$

BMI Formula (English)

$(lb \times 703) \div in^2$

Underweight BMI

Less than 18.5.

Normal BMI

18.5 to 24.9.

Overweight BMI

25.0 to 29.9.

Obese BMI

30.0 or higher.

Percent Change

$(New - Old) \div Old \times 100$

Nomogram

A chart used to estimate Body Surface Area (BSA).

BSA units

Square meters ($m^2$).

Pediatric Dosage by BSA

$(Child's BSA \div 1.73) \times Adult Dose$.

West's Nomogram

Used to calculate BSA for infants and children.

Leading Zero

Always use a zero before a decimal (e.g., 0.5 mg).

Trailing Zero

Never use a zero after a decimal (e.g., write 5 mg, not 5.0 mg).

Rounding

Usually round to the nearest tenth, but follow specific test instructions.

Converting lb to kg

Divide by 2.2.

Converting kg to lb

Multiply by 2.2.

Total Daily Dose

The total amount of drug taken in 24 hours.

Divided Doses

The amount of drug taken at each specific interval.

BID

Twice a day (every 12 hours).

TID

Three times a day (every 8 hours).

QID

Four times a day (every 6 hours).

QH

Every hour.

Q4H

Every four hours.

HS

At bedtime.

PRN

As needed.

NPO

Nothing by mouth.

Ad lib

As desired.

Stat

Immediately.

AC

Before meals.

PC

After meals.

PO

By mouth.

IV

Intravenous.

IM

Intramuscular.

ID

Intradermal.

SQ

Subcutaneous.

Solution

A mixture of a solute dissolved in a solvent.

Solute

The substance being dissolved (e.g., powder).

Solvent

The liquid used to dissolve the solute (e.g., water).

Concentration

The strength of a solution (ratio or percent).

Percentage

Parts per 100.