Concentrations & Compounding
Compounding calculations turn a prescribed strength into a quantity you can actually weigh, measure, or dilute. This is the largest group on PharmCalc: percentage and ratio strength, parts per million, specific gravity, the dilution equation, alligation, osmolarity, sodium chloride equivalents for isotonicity, and the mole and milliequivalent conversions underneath them. It also includes the minimum weighable quantity and aliquot planner, which answers a question the others assume away — whether your balance can weigh the quantity at all, and what to do when it cannot.
Percentage strength (w/v, v/v, w/w)
Convert between percentage strength, amount of solute, and total quantity for weight-in-volume, volume-in-volume, and weight-in-weight preparations.
Ratio strength
Convert between ratio strength (1 : X) and percentage strength for dilute preparations.
Parts per million (ppm)
Convert between parts per million, percentage strength, and ratio strength.
Specific gravity
Relate the weight and volume of a liquid through its specific gravity. Leave any one field blank to solve for it.
Dilution & concentration (Q₁C₁ = Q₂C₂)
Solve the dilution equation for any one of the four variables — leave the unknown blank.
Alligation (alternate)
Determine the proportions of a stronger and a weaker preparation needed to produce a desired intermediate strength.
Osmolarity (mOsmol/L)
Calculate the milliosmoles per litre contributed by a dissolved solute from its concentration, molecular weight, and number of dissociated particles.
Isotonicity — sodium chloride equivalent (E value)
Calculate a drug's sodium chloride equivalent and the amount of sodium chloride needed to make a solution isotonic.
Moles & millimoles
Convert between a mass of substance and the number of moles or millimoles it represents.
Milliequivalents from a salt weight
Convert between the weight of an electrolyte salt and the milliequivalents of ion it supplies.
Minimum weighable quantity & aliquot planner High-risk
Determine the smallest quantity a balance can weigh within an acceptable error, and plan an aliquot when the required amount falls below it.
High-consequence calculations in this group
These carry a greater risk of harm if the result is wrong or misapplied. Each states its own limits on its page; read them before acting on a number.
- Minimum weighable quantity & aliquot planner — Determine the smallest quantity a balance can weigh within an acceptable error, and plan an aliquot when the required amount falls below it.
Where to go next
- Practice problems — one worked problem for every calculator, solutions hidden until you open them.
- Reference tables and formula sheet — every constant and conversion factor used here, with citations.
- All 58 calculators — the full index, filterable by category.
Other categories
Also known as
percent strength · w/v · v/v · w/w · concentration · percent · strength · ratio · 1 in · 1:1000 · epinephrine 1:1000 · dilute solution · ppm · parts per million · fluoride · trace · water quality · SG · density · specific gravity · g/mL · weight to volume · dilution · Q1C1 · C1V1 · stock solution · concentrate · dilute · strengthen · alligation · mixing · two strengths · parts · alligation alternate · tic tac toe · osmolarity · osmolality · mOsm · tonicity · peripheral line · TPN osmolarity · E value · sodium chloride equivalent · isotonic · tonicity adjustment · ophthalmic · i factor · mole · mmol · molar · molecular weight · molarity · MW · mEq · milliequivalent · valence · electrolyte · potassium chloride · salt · MWQ · minimum weighable quantity · sensitivity requirement · aliquot · balance · USP 795