How to use the osmolarity calculator
Find the osmolarity of a salt or sugar solution. Enter concentration, particles per formula unit in the fields above; the osmolarity, tonicity vs blood (≈290) are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- c — Concentration (mmol/L)
- i — Particles per formula unit
Worked example
With concentration = 154 mmol/L, particles per formula unit = 2, the calculator gives osmolarity ≈ 308 mOsm/L; tonicity vs blood (≈290) ≈ Isotonic.
Frequently asked questions
What is the formula for the osmolarity calculation?
Osmolarity (mOsm/L) = c × i. Tonicity vs blood (≈290) = [Osmolarity]<270?"Hypotonic":([Osmolarity]>310?"Hypertonic":"Isotonic"). Here c is concentration (mmol/L), i is particles per formula unit.
What inputs do I need for the osmolarity calculator?
You need concentration in mmol/L, particles per formula unit. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.