Peptide Math Basics

Every calculator on this site rests on a few simple ideas: ratios, unit conversion and checking your answer. This guide explains them with plain arithmetic. It is not medical advice.

1. Ratios

A concentration is a ratio such as 5 mg per 2 mL. Dividing the top number by the bottom gives the amount per 1 mL: 5 ÷ 2 = 2.5 mg/mL.

2. Proportional thinking

If 1 mL holds 2.5 mg, then 2 mL holds 5 mg and 0.5 mL holds 1.25 mg. Doubling the volume doubles the amount at the same concentration.

3. Convert units first

Put everything in the same unit before dividing. 5 mg and 250 mcg cannot be divided directly. Convert 5 mg to 5000 mcg, then 5000 ÷ 250 = 20.

4. Work backwards to check

If the answer is 0.1 mL at 2500 mcg/mL, multiply back: 0.1 × 2500 = 250 mcg. If you get the number you started with, the arithmetic is consistent.

5. Sanity checks

A larger vial in the same volume gives a higher concentration.
More liquid gives a lower concentration.
A result 1000 times bigger or smaller than expected usually means mg and mcg were mixed up.

6. Rounding

Keep full numbers until the last step, then round once. Rounding early can move the final answer.

Worked example (mathematical example only)

10 mg in 4 mL is 2.5 mg/mL. A target of 500 mcg is 0.5 mg. Volume = 0.5 ÷ 2.5 = 0.2 mL, which is 20 units on a U-100 syringe. Check: 0.2 × 2.5 = 0.5 mg.

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Mathematical calculation only. Not medical advice.