Level Float Buoyancy Calculator
Check a spherical float for a level switch or magnetic level gauge: how deep it sinks in the liquid, the spare buoyancy force and the minimum specific gravity it can still float in.
- Displaced volume needed = m ÷ ρ = 120.2 cm³
- Spherical cap V(h) = πh²(3R − h) ÷ 3, solved for h: 37.25 mm
- Minimum SG = m ÷ (V × 1000) = 0.448
Float Buoyancy Formulas
Minimum SG = m ÷ (Vfloat × 1000 kg/m³)
Spare buoyancy = (Vfloat × ρ − m) × g
m is the float mass including magnet and stem parts that move with it, ρ the liquid density, R the float radius and Vfloat its total outer volume. The float floats only if the liquid SG is above the minimum SG; vendors usually require a margin.
Worked example
An 80 mm float of 120 g in water sinks about 37.3 mm (47 % of its diameter) and floats in liquids down to SG 0.448, with about 1.45 N of spare buoyancy.
Frequently Asked Questions
Why does the float sink depth matter?
It sets the offset between the liquid surface and the switch point or magnet position. The vendor calibrates for a stated density.
What happens if the liquid density changes?
The float rides higher or lower. In a magnetic level gauge this shifts the indicated level slightly.
How is an interface float designed?
Its density lies between the light and heavy liquid densities, so it settles at the interface.
Learn more on the blog
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