How It Works
This calculator works in 4 steps.
Enter the stock ratio strength
Type X for a 1:X stock, such as 1,000.
Enter the target ratio strength
Type the larger X of the weaker solution, such as 10,000.
Enter the final volume
Type the volume to prepare.
Read the stock volume
The calculator returns V₁ = V₂ × X₁ / X₂ and the % w/v and mg/mL forms.
The Formula
The formula uses the inverse relation between ratio X and concentration.
C (g/mL) = 1 / XV₁ / X₁ = V₂ / X₂% w/v = 100 / X- X₁ / X₂:
- Stock and target ratio terms (1:X)
- V₁ / V₂:
- Stock and final volumes
To make 10 mL of 1:10,000 (0.1 mg/mL) from 1:1,000 (1 mg/mL), V₁ = 10 × 1,000 / 10,000 = 1 mL. Add 9 mL diluent.
Conversion Table
The conversion table converts 6 ratio-strength pairs into percent and stock volume.
| Stock ratio | Stock % | Target ratio | Target % | Final volume | Stock volume |
|---|---|---|---|---|---|
| 1:1,000 | 0.1% | 1:10,000 | 0.01% | 10 mL | 1 mL |
| 1:100 | 1% | 1:1,000 | 0.1% | 100 mL | 10 mL |
| 1:1,000 | 0.1% | 1:200,000 | 0.0005% | 20 mL | 0.1 mL |
| 1:500 | 0.2% | 1:5,000 | 0.02% | 50 mL | 5 mL |
| 1:10 | 10% | 1:100 | 1% | 500 mL | 50 mL |
| 1:1,000 | 0.1% | 1:100,000 | 0.001% | 100 mL | 1 mL |
What Is the Ratio Strength Dilution Calculator?
The Ratio Strength Dilution Calculator is a pharmacy tool that dilutes solutions labeled as 1:X ratio strength, where 1:X means 1 g of solute in X mL of solution for solids in liquids. A 1:1,000 solution holds 1 g in 1,000 mL, which equals 0.1% w/v or 1 mg/mL.
Ratio strength appears on older drug labels and in pharmacy calculation exams. The calculator converts ratio strength to percent and mg/mL before solving, so the result is clear in modern units. Since 2016, the United States Pharmacopeia (USP) has required epinephrine labels to state mg/mL instead of ratio strength.
Common Uses
There are 5 main uses of this calculator.
Pharmacy exam practice
Students solve ratio-strength problems for licensing exams.
Legacy label reading
Pharmacists convert older 1:1,000 labels to mg/mL.
Compounding
Compounders dilute topical solutions written as ratio strength.
Veterinary products
Vet staff read ratio strengths on antiseptic concentrates.
Unit conversion
Users convert 1:X into % w/v, mg/mL, and ppm.