Pharmacy conversion chart

Updated

The complete US chart — metric, household, body weight, apothecary, temperature — with the 14 conversions the PTCE expects memorized marked, and a worked example on every trap row. Chart first, essay never.

Metric — mass

UnitEquivalentMust memorize
1 kg1,000 g
worked example

0.5 kg = 500 g — shift the decimal 3 places right

memorize
1 g1,000 mg
worked example

0.25 g = 250 mg — the classic trap: 0.025 g is 25 mg, not 250

memorize
1 mg1,000 mcg
worked example

0.125 mg = 125 mcg (levothyroxine strengths live here)

memorize

Metric — volume

UnitEquivalentMust memorize
1 L1,000 mL
worked example

2.5 L = 2,500 mL

memorize
1 dL100 mL

Lab values (mg/dL) — rarely a dispensing unit

Household

UnitEquivalentMust memorize
1 teaspoon (tsp)5 mL
worked example

2 tsp TID = 30 mL/day

memorize
1 tablespoon (tbsp)15 mL
worked example

1 tbsp BID = 30 mL/day → a 300 mL bottle lasts 10 days

memorize
1 fluid ounce (fl oz)30 mL (29.57 exact)
worked example

4 fl oz = 120 mL

memorize
1 cup240 mL (8 fl oz)memorize
1 pint480 mL convention (473 exact)
worked example

Pharmacy stock bottles: 16 fl oz × 30 = 480 mL

memorize
1 quart960 mL convention (946 exact)
1 gallon3,840 mL convention (3,785 exact)

Body weight & avoirdupois

UnitEquivalentMust memorize
1 kg2.2 lb
worked example

154 lb ÷ 2.2 = 70 kg — divide by 2.2 going to kg (mg/kg dosing)

memorize
1 oz28.35 g

Apothecary (legacy)

UnitEquivalentMust memorize
1 grain (gr)65 mg convention (64.8 exact)

Some older products use 60 mg per grain — check the label

worked example

gr v = 5 × 65 = 325 mg (aspirin/acetaminophen)

memorize
gr ss½ grain ≈ 32.5 mg

"ss" = semis, one half

Temperature

UnitEquivalentMust memorize
°F → °C(°F − 32) × 5⁄9
worked example

77 °F = (77 − 32) × 5/9 = 25 °C — room temperature storage

memorize
°C → °F°C × 9⁄5 + 32
worked example

2–8 °C (refrigerated) = 36–46 °F

memorize

Roman numerals (sig usage)

UnitEquivalentMust memorize
ss · i · v · x½ · 1 · 5 · 10
worked example

tabs iss = 1½ tablets

memorize
l · c · d · m50 · 100 · 500 · 1,000
Subtraction rulesmaller before larger subtracts
worked example

iv = 4, ix = 9, xl = 40

Exact factors: NIST SP 811 — guide for the use of SI units (exact factors) · verified 2026-08-03. Values marked “convention” are the rounded figures US pharmacy calculations (and the PTCE) expect.

Drill the chart

Unlimited conversion and temperature problems with instant grading and worked steps — reading a chart isn’t knowing it.

Temperature · difficulty 3/5

A vaccine refrigerator data logger reads 38°F. What is this in °C?

Printable PDF

The printable chart

A one-page laminate-style version of this chart — every table, the memorize marks, and the temperature formulas.

The on-page version stays free — no email needed to read it.

Common questions

How many mL are in a teaspoon, tablespoon, and ounce?

One teaspoon is 5 mL, one tablespoon is 15 mL, and one fluid ounce is 30 mL (29.57 exactly — pharmacy rounds to 30). These three cover most household-sig conversions on the exam; a cup is 8 fl oz = 240 mL.

How many mg are in a grain?

The dispensing convention is 65 mg per grain (64.8 exactly), so gr v = 325 mg — the classic aspirin strength. Some older product lines used 60 mg per grain; when a label states its own equivalence, the label wins.

How many pounds is a kilogram?

1 kg = 2.2 lb. Going from pounds to kilograms — the direction weight-based dosing needs — divide by 2.2: a 154 lb patient is 70 kg. Forgetting the conversion (or multiplying instead) is the classic mg/kg trap.

How do you convert °F to °C for storage?

°C = (°F − 32) × 5⁄9. The storage ranges worth memorizing: refrigerated 2–8 °C (36–46 °F), controlled room temperature 20–25 °C (68–77 °F), and freezer −25 to −10 °C. Vaccine-handling questions live on these numbers.

What conversions does the PTCB exam test?

The 14rows marked “memorize” above: metric prefix shifts (kg–g–mg–mcg), household volumes (tsp/tbsp/oz/cup), kg↔lb, the grain, and both temperature formulas. They appear inside Order Entry & Processing (22.5% of the exam) rather than as standalone trivia.