Tonicity Calculator

Work out tonicity instantly with clear inputs, formula shown and shareable results.

About Tonicity Calculator

Compares external and intracellular osmolarity to classify the solution as hypotonic, isotonic or hypertonic and predict the direction of water movement.

Formula

Tonicity

Gradient = external osmolarity - intracellular osmolarity; water moves down its own concentration gradient towards the higher solute concentration

Worked example

With the default values below, Tonicity Calculator returns Tonicity of Hypotonic — water enters the cell, which swells. Change any input above and every figure here is recalculated in your browser.

Inputs used

Solution osmolarityaccepts 0–2,000 mOsm/L: 250 mOsm/L
Intracellular osmolarityaccepts 50–1,000 mOsm/L: 300 mOsm/L

Results

Tonicity: Hypotonic — water enters the cell, which swells
Osmotic gradient: -50.00 mOsm/L
Solution to cell osmolarity ratio: 0.8333
Direction of water movement: Into the cell

Step by step

1Values used
2Tonicity
3Tonicity= Hypotonic — water enters the cell, which swells
4Osmotic gradient= -50.00 mOsm/L
5Solution to cell osmolarity ratio= 0.8333
6Direction of water movement= Into the cell

Assumptions and limits

The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Is tonicity the same as osmolarity?

No. Tonicity counts only solutes that cannot cross the membrane, so urea raises osmolarity without raising tonicity.

What happens in a very hypotonic solution?

Animal cells lyse; plant cells become turgid because the cell wall resists further expansion.