Surface Tension Calculator
Estimate a liquid’s surface tension using the classic capillary rise method, based on how high the liquid climbs a narrow tube.
What surface tension is
Surface tension is the tendency of a liquid’s surface to behave like a stretched elastic sheet, caused by cohesive forces between its molecules. It’s why water beads up, why insects can walk on ponds, and why liquid climbs up a thin tube against gravity — a phenomenon called capillary action.
How this calculator works
This tool uses the capillary rise method, one of the standard ways to measure surface tension in a physics lab. When a narrow tube is dipped into a liquid, the liquid rises (or falls) to a height where the upward pull of surface tension balances the weight of the risen column. This gives the formula gamma = (density x gravity x height x radius) / (2 x cos(contact angle)), where the contact angle describes how the liquid meets the tube wall (0° for a liquid that wets the tube completely, like water in clean glass).
Enter the liquid’s density, how high it rises in the tube, the tube’s inner radius, and the contact angle if known (0° is a reasonable default for water in glass). This is a standard physics reference calculation for general educational use; real lab measurements should account for tube cleanliness, temperature, and measurement precision.