Ratio strength and percentage converter

A ratio strength of 1 in N means 1 gram in N millilitres, so the percentage is 100 divided by N and the concentration in mg/mL is 1000 divided by N. Adrenaline 1:1000 is therefore 1 mg/mL and 1:10,000 is 0.1 mg/mL, a tenfold difference between near-identical labels.

When to use the ratio strength calculator

Use whenever a product is labelled by ratio rather than percentage, which is still common for adrenaline and some older preparations, and whenever a question mixes the two notations.

The ratio strength formula

A ratio strength of 1 in N means 1 g in N mL. Percentage w/v = (1 ÷ N) × 100. Concentration in mg/mL = 1000 ÷ N.

Worked example

Adrenaline 1:1000 means 1 g in 1000 mL, which is 0.1% w/v and 1 mg/mL. A 10 mL ampoule therefore contains 10 mg.

The mistake that costs marks

Ratio strength always means grams per millilitres for solutions, so 1:1000 is 1 mg/mL and 1:10,000 is 0.1 mg/mL. Confusing the two is the classic adrenaline error, and the tenfold difference between them is the reason the notation is being phased out in favour of mg/mL.

Study aid, not a clinical tool

This calculator exists so you can learn the method and check your working for an examination. It is not medical advice and not clinical decision support, and it must not be used to make a decision about a real patient. Verify any result against your local formulary, the product literature and a qualified pharmacist. Our medical disclaimer sets out the full position.

Calculators you will usually need alongside this

Most questions that reach for one of these reach for another a step later, so these are the three that most often pair with it.

• Dilution calculator (C1V1 = C2V2) — Dilution
• Alligation calculator — Alligation
• Milliequivalent and millimole converter — mEq and mmol

Keep going

Calculations are only half of what examinations test. The other half is knowing why a drug does what it does, which is what decides whether a number you calculated is even the right number to be calculating. Start with Best pharmacy calculators. The drug class pages cover the mechanism behind the number, or browse the rest of the free calculators and try the practice questions.