Clinical Conversions Reference | Wahero Health Institute

Correct this one first

"1 teaspoon = 5 ounces" is wrong, and it circulates constantly

1 tsp = 5 oz → 1 tsp ≈ 0.17 oz

The 5 is real and the unit is wrong. A teaspoon is 5 millilitres, not 5 ounces. Five ounces is roughly 148 mL, which is most of a cup, so the error is not small: it is a factor of about thirty.

1 tsp = 5 mL (the convention used in medicine)
1 fl oz ≈ 29.57 mL

So 1 oz in teaspoons = 29.57 ÷ 5 ≈ 5.91 tsp, usually rounded to 6
And 1 tsp in ounces = 5 ÷ 29.57 ≈ 0.17 oz

Show the arithmetic rather than memorising the answer. A conversion you can derive survives a tired night shift. One you memorised does not.

Mass: grams, milligrams, micrograms

Conversion	Value	Example
1 gram (g)	1,000 milligrams (mg)	2,500 mg = 2.5 g
1 milligram (mg)	1,000 micrograms (mcg)	0.5 mg = 500 mcg
1 gram (g)	1,000,000 micrograms (mcg)	2,500 mg = 2,500,000 mcg

Direction check. Going to a bigger unit, divide. Going to a smaller unit, multiply. If your answer has moved the decimal point the wrong way you will usually be out by exactly a factor of a thousand, which is the commonest and most dangerous size of error in this whole subject.

Volume

Conversion	Value	Note
1 cc	1 mL	Exactly equal. See the abbreviations warning below
1 fluid ounce (oz)	≈ 29.57 mL	Rounded to 30 mL for patient teaching
1 teaspoon (tsp)	5 mL	A convention. The US legal teaspoon is 4.93 mL
1 tablespoon (tbsp)	15 mL	Three teaspoons
1 cup	≈ 240 mL	Eight ounces, rounded
1 litre (L)	1,000 mL	The standard IV fluid bag

Weight

Conversion	Value	Example
1 kilogram (kg)	2.20462 pounds (lb)	5 kg = 11.02 lb
Everyday shortcut	kg × 2.2	10 kg ≈ 22 lb
Pounds to kilograms	lb ÷ 2.2	154 lb = 70 kg

Why this one matters more than it looks. Weight-based doses are calculated in kilograms. A patient weight recorded in pounds and used as kilograms produces a dose more than twice what was intended. Convert first, and write the unit down every single time.

Temperature

Fahrenheit to Celsius: °C = (°F − 32) × 5/9 | Celsius to Fahrenheit: °F = (°C × 9/5) + 32

Worked: convert 68°F
(68 − 32) × 5/9 = 36 × 5/9 = 180 ÷ 9 = 20°C

Fahrenheit	Celsius	Anchor
32°F	0°C	Freezing
68°F	20°C	Room temperature
98.6°F	37°C	Normal body temperature
212°F	100°C	Boiling

Household equivalents for patient teaching

These are the approximations you give a patient at discharge. They are deliberately rounded, because a patient measuring at home with a kitchen spoon is not working to two decimal places. Use a proper oral syringe or dosing cup wherever one is available.

Metric	Household
5 mL	1 teaspoon
15 mL	1 tablespoon
30 mL	1 ounce
240 mL	1 cup
1 kg	2.2 pounds

The units you will meet, and what they are for

Unit	Used for
kg	Patient weight, and the basis of all weight-based dosing
g	Larger doses and supplies
mg	Most oral and IV medications
mcg	Potent and high-alert medications
ng	Laboratory values, for example serum drug levels reported in ng/mL
mL	Oral liquids, injections, IV volumes
gtt	Drops. Gravity IV drip rates, eye and ear drops
mg/kg	Weight-based dosing
mcg/kg/min	Titrated infusions in critical care
mg/mL	Concentration of a medication in a vial
% solution	IV fluids, for example 5% dextrose or 0.9% sodium chloride
mEq/L	Electrolytes
mL/hr	Infusion pump rate
gtt/min	Gravity drip rate

Three abbreviations you will see written, and should never write yourself. The Institute for Safe Medication Practices maintains a list of error-prone abbreviations, and these three are on it. You need to recognise them, because they appear on older charts and labels. You should not reproduce them.

U for unit. Handwritten, it is misread as a zero or a four, which turns 4U into 40. Write unit in full.
IU for international unit. Misread as IV or as 10. Write international unit in full.
cc for cubic centimetre. It equals 1 mL exactly, but handwritten it is misread as u. Write mL.

Two number habits that prevent tenfold errors.

Always a leading zero: write 0.5 mg, never .5 mg. A missed decimal point turns .5 into 5.
Never a trailing zero: write 5 mg, never 5.0 mg. A missed decimal point turns 5.0 into 50.

Educational use. This page is learning material for nurses and nursing students. It is not clinical advice, and it does not replace your employer's policies, your facility's protocols, or the judgement of a licensed clinician. Always follow the standards and procedures in force where you practise. Always double check units before administering anything, and use your facility's independent double check for high alert medications such as insulin, heparin, opioids and chemotherapy.

Conversions are the easy half

Rates are where people actually lose marks. Three hours on gtt/min and mL/hr, ending in a validation on real tubing against a timed minute.

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