Household Measurements

While the metric system is standard in clinical settings, nurses frequently encounter household measurements when:

• Taking medication histories from patients
• Instructing patients on home medication administration
• Working with liquid medications measured by spoon or cup

Understanding how household units relate to metric units is essential for patient education and safe home care instructions.

Common Household Units

Volume

Household Unit	Abbreviation	Metric Equivalent
teaspoon	tsp	5 mL
tablespoon	tbsp	15 mL
fluid ounce	fl oz	30 mL
cup	c	240 mL
pint	pt	480 mL
quart	qt	960 mL

Weight

Household Unit	Abbreviation	Metric Equivalent
ounce	oz	30 g
pound	lb	453.6 g
pound	lb	0.454 kg

Conversion Factors

Every household-to-metric relationship is also a factor pair:

\[\frac{5 \text{ mL}}{1 \text{ tsp}} \quad \text{or} \quad \frac{1 \text{ tsp}}{5 \text{ mL}}\]

\[\frac{15 \text{ mL}}{1 \text{ tbsp}} \quad \text{or} \quad \frac{1 \text{ tbsp}}{15 \text{ mL}}\]

\[\frac{2.2 \text{ lb}}{1 \text{ kg}} \quad \text{or} \quad \frac{1 \text{ kg}}{2.2 \text{ lb}}\]

Choose the orientation that puts the unit you want on top and the unit you have on the bottom.

Example — tsp to mL: You have 3 tsp and want mL. Put mL on top:

\[3 \cancel{\text{ tsp}} \times \frac{5 \text{ mL}}{1 \cancel{\text{ tsp}}} = 15 \text{ mL}\]

Example — lb to kg: You have 132 lb and want kg. Put kg on top:

\[132 \cancel{\text{ lb}} \times \frac{1 \text{ kg}}{2.2 \cancel{\text{ lb}}} = 60 \text{ kg}\]

Key Weight Conversion

\[1 \text{ kg} = 2.2 \text{ lb}\]

This is an important household-to-metric weight conversion.

Tips

Weight Shortcut

Divide by 2.2 to convert lb to kg.

Multiply by 2.2 to convert kg to lb.

Check your Results

Converting from a larger unit to a smaller unit should produce a larger number.

Converting from a smaller unit to a large unit should produce a smaller number.

For example, 100 kg = 220 lbs. Pounds are a smaller unit than kilograms so the resulting number is larger.

Conversely, 200 mL = 0.2 L. Liters are a larger unit than mL, so the resulting number is smaller.

Patient Education

Spoon Sizes Vary

Household spoons are not standardized. A kitchen teaspoon may hold anywhere from 3 to 7 mL. Always instruct patients to use a calibrated measuring device — oral syringe, medicine cup, or dosing spoon — rather than a kitchen spoon.

Documenting Intake

In clinical settings, fluid intake is always documented in mL, never in household units. Convert any household measurements before recording.

Practice Problems

Problem 1

A patient takes 3 teaspoons of cough syrup. Convert to mL.

Answer

\[3 \text{ tsp} \times 5 \text{ mL/tsp} = 15 \text{ mL}\]

Problem 2

Convert 88 lb to kg.

Answer

\[88 \text{ lb} \div 2.2 = 40 \text{ kg}\]

Problem 3

A patient needs to take 45 mL of an oral solution at home. How many tablespoons is that?

Answer

\[45 \text{ mL} \div 15 \text{ mL/tbsp} = 3 \text{ tbsp}\]

Problem 4

Convert 60 kg to lb.

Answer

\[60 \text{ kg} \times 2.2 = 132 \text{ lb}\]

Problem 5

A child weighs 44 lb. A weight-based antibiotic is ordered at 10 mg/kg. What is the child's weight in kg and what is the dose?

Answer

Step 1 — Convert weight: [44 \text{ lb} \div 2.2 = 20 \text{ kg}]

Step 2 — Calculate dose: [10 \text{ mg/kg} \times 20 \text{ kg} = 200 \text{ mg}]

Clinical Tip

Always obtain and document patient weight in kg in clinical settings. If a patient gives their weight in pounds, convert immediately and record in kg to avoid confusion during weight-based dosing calculations.