Surface Tension Converter
Surface tension is a force per unit length, the SI unit being the newton per meter (N/m). In practice it is usually quoted in millinewtons per meter (mN/m) or the equivalent CGS unit dyne per centimeter (dyn/cm); for water at room temperature it is about 72 mN/m. This converter moves a value between N/m, mN/m, dyn/cm, and pound-force per foot, reducing everything to N/m as a common base. The factors are exact: 1 mN/m equals 0.001 N/m, 1 dyn/cm equals 0.001 N/m, and 1 lbf equals 4.4482216152605 N over 0.3048 m.
Surface tension conversion
Base value (N/m) = input * factor(from unit)
Output = base value / factor(to unit)
1 mN/m = 0.001 N/m
1 dyn/cm = 0.001 N/m
1 lbf/ft = 4.4482216152605 / 0.3048 N/m
Surface tension and surface energy per area share the same SI dimension, so erg/cm2 equals dyn/cm equals 0.001 N/m.
Surface tension context
- The SI unit of surface tension is the newton per meter (N/m), equal to a joule per square meter.
- Water at about 20 degrees Celsius has a surface tension near 72 mN/m.
- The CGS dyne per centimeter is numerically equal to the millinewton per meter.
- Surface energy per unit area (erg/cm2) shares the same dimension as surface tension.
- The pound-force per foot is the customary unit, with 1 lbf defined as 4.4482216152605 N.
Surface tension: frequently asked questions
Why are dyn/cm and mN/m equal?
One dyne is 1e-5 newtons and one centimeter is 0.01 meters, so 1 dyn/cm equals 1e-5 N divided by 0.01 m, which is 0.001 N/m. A millinewton per meter is also 0.001 N/m, so the two units are numerically identical. Water near room temperature is about 72 in both.
What is the SI unit of surface tension?
The newton per meter (N/m), which is dimensionally equivalent to the joule per square meter (J/m2). The latter form emphasizes that surface tension is also a surface energy per unit area.
How do I convert lbf/ft to N/m?
One pound-force is defined as 4.4482216152605 newtons and one foot is 0.3048 meters, so 1 lbf/ft equals 4.4482216152605 divided by 0.3048, about 14.5939 N/m. The converter applies this exact factor.
Is erg/cm2 the same as dyn/cm?
Yes. An erg per square centimeter is a surface energy density, and a dyne per centimeter is a force per length; both reduce to 0.001 N/m, so they are interchangeable for surface tension or surface energy.
What are the conversion factors based on?
They follow the SI definitions documented by NIST and BIPM: the newton, meter, dyne (1e-5 N), centimeter (0.01 m), and the customary pound-force (4.4482216152605 N) and foot (0.3048 m).
Official sources
- NIST Special Publication 811: Guide for the Use of the International System of Units.
- BIPM: SI Units.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.