Ratio Strength Calculator (1:1000 to % and mg/mL)

How it works

ratio 1:x (w/v) = 1 g in x mL · mg/mL = 1,000 ÷ x · % w/v = 100 ÷ x = mg/mL ÷ 10 · x = 100 ÷ % · mcg/mL = mg/mL × 1,000 · ppm (mg/L) = mg/mL × 1,000

Ratio strength expresses a weak concentration as one part of drug in a total number of parts: for solids in liquids, 1:1,000 means 1 g in 1,000 mL. It is still printed on epinephrine (adrenaline) ampoules and local anesthetics with epinephrine, and confusing 1:1,000 with 1:10,000 is a well-known cause of tenfold dosing errors — which is why many countries now label epinephrine in mg/mL as well. Percent strength is grams per 100 mL, so dividing 100 by the ratio number gives the percent and dividing 1,000 by it gives mg/mL.

Worked example

Epinephrine 1:1,000 contains 1 g in 1,000 mL, which is 1 mg/mL (1,000 mcg/mL), a percent strength of 0.1% w/v and 1,000 ppm. Diluting it tenfold gives 1:10,000, or 0.1 mg/mL.

Sources: ISMP — Petition to USP on epinephrine labeling (ratio expressions) · ASA — FDA requires replacing ratio expressions with mg/mL on epinephrine labels (2017) · Wikipedia — Concentration (mass concentration and ratio)

Frequently asked questions