Dose by weight calculator
From a weight, a dose in mg/kg and the strength of what you are drawing from, to the volume in the syringe.
Free, no account needed. Nothing you type is sent anywhere or stored — the arithmetic runs in your browser.
Inputs
Results
Volume to draw
8.3µL
Check this against the syringe graduations before drawing.
- Drug required
- 0.0025mg
The two steps
First the mass of drug: dose × weight, with the units lined up — mg/kg against grams means dividing by a thousand. Then the volume: mass ÷ stock concentration. A 25 g mouse at 0.1 mg/kg needs 0.0025 mg, which from a 0.3 mg/mL stock is about 8.3 µL.
The mistake this is worth catching
Many labs keep a shortcut instead: a factor in microlitres per gram of body weight, so a 25 g mouse gets 500 µL and nobody does the arithmetic. It works until somebody makes the stock up differently.
That factor has a concentration baked into it. Remake the stock at half strength and the factor still says 500 µL, the syringe still looks right, and the animal gets half the dose — with nothing on paper to show it. If you keep a factor, write down the concentration it assumes, and check it whenever a bottle is remade.
Before you draw
Check the volume against the graduations on the syringe you actually have. A number that cannot be measured accurately is not a usable dose, and very small volumes usually mean the stock wants diluting rather than the plunger being read more carefully.
This works out arithmetic. It does not decide what dose is appropriate — that comes from your approved animal protocol and your veterinarian, and this calculator has no idea what species, route or drug you have in mind.