Dilution
When the vial is already too strong.
Reconstitution is a one-time choice. If it left you with a dose that measures two units on the barrel, this works out how to dilute what you have rather than write the vial off.
- Method
- C1V1 = C2V2
- Cost
- Free
- Signup
- None
- Data
- Nothing stored
The science
The fix for a vial that is already too strong
01
Reconstitution happens once per vial and cannot be undone. If you added one millilitre to a 10 mg vial and your dose now works out to two units on the barrel, the vial is not wrong, it is simply too concentrated to measure accurately at that dose. Dilution is the remedy.
02
The arithmetic is the standard dilution relationship, that concentration times volume is conserved. Written out, the concentration you have multiplied by the volume you draw equals the concentration you want multiplied by the final volume. Rearranged, the volume of stock to draw is the target concentration times the final volume, divided by the concentration you started with.
03
In practice you draw that volume of your existing solution into a fresh sterile vial, then add bacteriostatic water until you reach the final volume. A tenfold dilution means one part stock to nine parts water, and the calculator above gives both figures so there is no need to derive the ratio.
04
There is a limit worth knowing. If the calculated volume of stock falls below two units, you cannot measure it accurately either, and you have moved the measurement problem rather than solved it. Raising the final volume increases how much stock you draw and brings it back into a readable range, which is why that field exists.
Common ratios
The dilutions people actually need
Most cases are a two, five or tenfold reduction. These are the parts of stock to parts of water for each, which is worth recognising as a sanity check on any figure a calculator hands you.
| Factor | Stock | Water | 10 mg/ml becomes | mcg per unit |
|---|---|---|---|---|
| 2× | 1 part | 1 part | 5 mg/ml | 50 mcg |
| 2.5× | 2 parts | 3 parts | 4 mg/ml | 40 mcg |
| 4× | 1 part | 3 parts | 2.5 mg/ml | 25 mcg |
| 5× | 1 part | 4 parts | 2 mg/ml | 20 mcg |
| 10× | 1 part | 9 parts | 1 mg/ml | 10 mcg |
A tenfold dilution is one part stock to nine parts water, not one to ten. The factor counts the final volume, so the water is always one part fewer than the factor. That single off-by-one accounts for most dilutions that come out wrong.
FAQ
Common questions
How do you dilute a peptide that is too concentrated?
Work out the volume of your existing solution to draw using the dilution relationship: target concentration times final volume, divided by your current concentration. Draw that much stock into a fresh sterile vial, then add bacteriostatic water up to the final volume. The calculator above does the arithmetic and also tells you how much water that means.
What is the difference between reconstitution and dilution?
Reconstitution adds liquid to a dry powder, turning a mass into a solution, and it happens once per vial. Dilution takes a solution that already exists and reduces its concentration by adding more liquid. You reach for dilution when a vial was reconstituted too concentrated to dose accurately and starting over is not an option.
What is the C1V1 equals C2V2 formula?
It states that the amount of substance is unchanged by dilution: concentration multiplied by volume is the same before and after. C1 and V1 are the concentration and volume you draw from your stock, C2 and V2 the concentration and volume you finish with. Solved for V1, it gives the volume of stock to draw, which is what the calculator returns.
Can I dilute directly inside the original vial?
Only if the vial has headroom and you intend to dilute the entire contents, which changes the concentration of everything in it. Diluting a measured portion into a separate sterile vial is the more usual approach because it leaves the original solution intact. Either way the calculation is the same, and the container is a practical question rather than a mathematical one.
Does diluting a peptide make it less effective?
Dilution changes concentration, not the amount of peptide in a given dose. Draw twice the volume at half the concentration and you have drawn the same amount. What dilution genuinely affects is stability and contamination risk, since you are adding liquid and entering vials again, so it is worth doing once and deliberately rather than repeatedly.
Why does the calculator warn about drawing under two units?
Because a U-100 barrel cannot measure that reliably, and a dilution that requires an unmeasurable starting volume has relocated the problem instead of fixing it. Increasing the final volume raises the amount of stock you draw. That is the adjustment to make when the warning appears.
VialClock
This page calculates. Your notes app forgets.
Every tool here is stateless by design. What it cannot do is remember that your vial was mixed eleven days ago, or that a step-up is due this week.
Browse all calculatorsThis tool performs arithmetic on figures you enter, or presents a manufacturer-published schedule. It does not know your protocol, will never suggest a dose, and is not medical advice. Dosing decisions belong with a qualified prescriber.