Reference tables & formula sheet

Every constant, conversion factor, and equivalency used anywhere in PharmCalc, in one place. This page is designed to print as a usable formula sheet — use your browser's print command.

Measurement conversions

Volume

Apothecary/household equivalents as conventionally used in US pharmacy practice; USP <1221> household measure guidance.
Unit	In mL	Note
millilitre (mL)	1
litre (L)	1,000
teaspoonful (tsp)	5	Pharmacy convention: 1 tsp = 5 mL.
tablespoonful (tbsp)	15	Pharmacy convention: 1 tbsp = 15 mL = 3 tsp.
fluid ounce (fl oz)	30	Pharmacy convention 30 mL; exact US fl oz = 29.5735 mL.
cup	240	1 cup = 8 fl oz.
pint (pt)	480	1 pint = 16 fl oz.
quart (qt)	960	1 quart = 2 pints.
gallon (gal)	3,840	1 gallon = 4 quarts; exact US gal = 3785.41 mL.

Weight

Avoirdupois/metric equivalents as conventionally used in US pharmacy practice.
Unit	In g	Note
microgram (mcg)	0.000001
milligram (mg)	0.001
gram (g)	1
kilogram (kg)	1,000	1 kg = 2.2 lb (practice convention; exact 2.20462 lb).
grain (gr)	0.065	Pharmacy convention: 1 grain = 65 mg; exact 64.79891 mg.
ounce (oz, avdp)	28.4	Pharmacy convention 28.4 g; exact avoirdupois oz = 28.3495 g.
pound (lb)	454	Pharmacy convention 454 g; exact 453.592 g.

Length

Exact definition: 1 inch = 2.54 cm (international yard and pound agreement, 1959).
Unit	In cm	Note
millimetre (mm)	0.1
centimetre (cm)	1
metre (m)	100
inch (in)	2.54
foot (ft)	30.48

Temperature

°C = (°F − 32) ÷ 1.8 · °F = (°C × 1.8) + 32

Milliequivalents and millimoles

Monovalent ions convert 1 : 1. Divalent ions convert 1 : 0.5 (1 mmol = 2 mEq). Phosphate is dosed in millimoles of phosphorus and must not be converted using a fixed valence.

Core formulae

Quantity	Formula
Percentage strength	% = (solute ÷ total) × 100 · w/v uses g/100 mL, v/v mL/100 mL, w/w g/100 g
Ratio strength	% strength = 100 ÷ ratio strength
Parts per million	ppm = % × 10,000
Specific gravity	SG = weight (g) ÷ volume (mL)
Dilution	Q₁ × C₁ = Q₂ × C₂
Alligation	parts of high = desired − low · parts of low = high − desired
Osmolarity	mOsmol/L = (g/L ÷ MW) × particles × 1000
Sodium chloride equivalent	E = (58.5 × i) ÷ (MW × 1.8)
Moles / millimoles	mol = g ÷ MW · mmol = mg ÷ MW
Milliequivalents	mEq = (mg × valence) ÷ MW · mEq = mmol × valence
Minimum weighable quantity	MWQ = sensitivity requirement ÷ acceptable error rate
Body mass index	BMI = kg ÷ m² · (lb ÷ in²) × 703
Ideal body weight	male 50 kg + 2.3 × (in over 5 ft) · female 45.5 kg + 2.3 × (in over 5 ft)
Adjusted body weight	AdjBW₀.₄ = IBW + 0.4 × (TBW − IBW)
Body surface area (Mosteller)	BSA = √[Ht(cm) × Wt(kg) ÷ 3600]
Creatinine clearance (Cockcroft–Gault)	CrCl = [(140 − age) ÷ (72 × SCr)] × wt(kg) × 0.85 if female
Maintenance fluid (>20 kg)	1500 mL + 20 mL × (kg − 20) · or 30–40 mL/kg/day
Drip rate	gtt/min = (gtt/mL) × (mL/hr) ÷ 60
Dehydration indicator	BUN : SCr > 20 : 1
Enteral calories	carbohydrate 4 · protein 4 · fat 9 kcal/g
Parenteral calories	dextrose monohydrate 3.4 · amino acid 4 kcal/g · ILE 10% 1.1, 20% 2.0, 30% 3.0 kcal/mL
Nitrogen from protein	N (g) = protein (g) ÷ 6.25
Total energy expenditure	TEE = BEE × activity factor × stress factor
Bioavailability	F (%) = 100 × (AUC_ev ÷ AUC_iv) × (Dose_iv ÷ Dose_ev)
Volume of distribution	Vd = amount in body ÷ plasma concentration
Clearance	Cl = (F × dose) ÷ AUC · Cl = ke × Vd
Elimination rate constant	ke = Cl ÷ Vd · ke = ln(C₁/C₂) ÷ t
Half-life	t½ = 0.693 ÷ ke
Concentration prediction	C₂ = C₁ × e^(−ke·t)
Loading dose	LD = (desired concentration × Vd) ÷ F
Mean arterial pressure	MAP = [(2 × diastolic) + systolic] ÷ 3
Anion gap	AG = Na − Cl − HCO₃
Corrected calcium	Ca_corr = Ca + [(4.0 − albumin) × 0.8]
Corrected phenytoin	C_corr = total ÷ [(0.2 × albumin) + 0.1]
Absolute neutrophil count	ANC = WBC × [(% segs + % bands) ÷ 100]
Henderson–Hasselbalch	weak acid pH = pKa + log([salt]/[acid]) · weak base pH = pKa + log([base]/[salt])
Percent ionisation	acid 100 ÷ (1 + 10^(pKa−pH)) · base 100 ÷ (1 + 10^(pH−pKa))
Risk / RR / RRR / ARR	risk = events ÷ n · RR = risk_tx ÷ risk_ctl · RRR = (ctl − tx) ÷ ctl · ARR = ctl − tx
NNT / NNH	NNT = 1 ÷ ARR (ARR as a decimal), always rounded up
Odds ratio	OR = (A × D) ÷ (B × C)
Hazard ratio	HR = hazard rate treatment ÷ hazard rate control
Incremental cost-effectiveness	ICER = (C₂ − C₁) ÷ (E₂ − E₁)
Insulin total daily dose	TDD = weight (kg) × 0.5 units/kg/day; half basal, half rapid split across meals
Insulin-to-carbohydrate ratio	450 ÷ TDD (regular) · 500 ÷ TDD (rapid-acting)
Correction factor	1500 ÷ TDD (regular) · 1800 ÷ TDD (rapid-acting)
Correction dose	(current glucose − target glucose) ÷ correction factor
Friedewald	LDL = TC − HDL − (TG ÷ 5); invalid above TG 400 mg/dL
Pack-year history	pack-years = (cigarettes per day ÷ 20) × years smoked
Time to burn	TTB with sunscreen = SPF × TTB without

Therapeutic equivalency

Systemic corticosteroids

Approximate glucocorticoid equipotent doses as conventionally tabulated; mineralocorticoid activity, half-life, and route differ between agents and are not captured by dose equivalence alone.
Agent	Equivalent dose (mg)
Cortisone	25
Hydrocortisone	20
Prednisone	5
Prednisolone	5
Methylprednisolone	4
Triamcinolone	4
Dexamethasone	0.75
Betamethasone	0.6

HMG-CoA reductase inhibitors

Approximately LDL-equivalent daily doses. This is a potency comparison only — it is NOT an intensity-of-therapy classification. For intensity, see the 2018 AHA/ACC/Multisociety Cholesterol Guideline (Grundy SM et al. Circulation. 2019;139:e1082-e1143).
Agent	Equivalent dose (mg)
Pitavastatin	2
Rosuvastatin	5
Atorvastatin	10
Simvastatin	20
Lovastatin	40
Pravastatin	40
Fluvastatin	80

Loop diuretics

Approximate equipotent oral doses. Bioavailability of oral furosemide is variable (~10–100%), which underlies its 1:2 IV:PO ratio.
Agent	Equivalent dose (mg)
Ethacrynic acid	50
Furosemide	40
Torsemide	20
Bumetanide	1

Route conversions

Route conversion ratios as conventionally applied; confirm against current product labelling and institutional protocol.
Drug	IV : PO
Metoprolol	IV : PO = 1 : 2.5
Levothyroxine	IV : PO = 0.75 : 1 (IV dose ≈ 75% of oral dose)
Furosemide	IV : PO = 1 : 2
Bumetanide / torsemide / ethacrynic acid	IV : PO = 1 : 1

Other drug-dose conversions

Aminophylline ↔ theophylline	Aminophylline → theophylline: × 0.8. Theophylline → aminophylline: ÷ 0.8. Mnemonic: ATM.
Calcium salts	Calcium carbonate = 40% elemental calcium. Calcium citrate = 21%.
Potassium chloride	KCl 10% oral solution = 20 mEq per 15 mL.
Lithium	5 mL lithium citrate syrup = 300 mg lithium carbonate = 8 mEq Li⁺.
Insulin	Generally 1 : 1. NPH twice daily → glargine daily: use 80% of the NPH TDD. Toujeo → other glargine: use 80%.

Reference intervals used

Conventional values. Your own laboratory's reported ranges take precedence over any of these.
Measure	Range	Source note
Arterial pH	7.35 – 7.45	Conventional arterial blood gas reference intervals; verify against your laboratory's reported ranges.
pCO₂	35 – 45 mmHg
HCO₃	22 – 26 mEq/L
Anion gap	3 – 11 mEq/L	Reference interval varies by laboratory and by whether potassium is included. Albumin correction: Figge J et al. J Lab Clin Med. 1998;131(3):249-259.
Corrected calcium	8.5 – 10.5 mg/dL	Laboratory-specific.
Phenytoin (total)	10 – 20 mcg/mL	Free phenytoin 1 – 2 mcg/mL.
ANC — severe neutropenia	< 500 cells/mm³	Common Terminology Criteria for Adverse Events (CTCAE) v5.0 neutrophil count decreased.
MAP — sepsis target	≥ 65 mmHg	Surviving Sepsis Campaign 2021.
Theophylline	5 – 15 mcg/mL	Narrow therapeutic index.
Lithium (maintenance)	0.6 – 1.0 mEq/L	Acute mania 0.8 – 1.2 mEq/L; toxicity generally above 1.5.

PharmCalc 1.2.0