Buoyancy Experiment Calculator — Weight in Air vs Fluid
Replicate the classic Archimedes spring-scale experiment: weigh an object in air, then weigh it fully submerged in a fluid. The weight lost equals the buoyant force, and from that you can determine the displaced volume and the object's own density.
N
N
Fluid
m/s²
Weight lost in fluid = upward buoyant force (Archimedes' principle)
- 1
Weight in air
0.98 - 2
Apparent weight in fluid
0.588 - 3
Buoyant force = weight lost
0.98 − 0.588 = 0.392The fluid's upward push equals the weight the object loses when submerged (Archimedes' principle).
How does this calculator work?
Weigh an object in air and again when fully submerged. The weight lost equals the buoyant force (F_b = W_air − W_fluid). Divide by fluid density × g to get displaced volume, then divide object mass by that volume to find the object's density — all from two scale readings.
Formula
How this is calculated
When an object is hung on a spring scale and submerged in a fluid, its apparent weight decreases because the fluid pushes up on it. The difference between the true weight (in air) and the apparent weight (in fluid) is exactly the buoyant force: F_b = W_air − W_fluid.
Because F_b = ρ_fluid × V_displaced × g (Archimedes' principle), the volume of fluid displaced is V = F_b / (ρ_fluid × g). If the object is fully submerged, this also equals the object's volume, so the object's density is its mass divided by that volume: ρ_object = (W_air / g) / V.
This experiment only works when the object is completely underwater and does not dissolve or react with the fluid. The result is most accurate when the spring scale reads to at least three significant figures and the object is large enough that surface-tension effects on the string are negligible.
Frequently asked questions
Because the fluid exerts an upward buoyant force, reducing what the spring scale reads. If the object is denser than the fluid it will still sink, but its apparent weight will be lighter. If the 'apparent' reading equals or exceeds the air weight, the object is floating or the measurements are inconsistent.
Yes — that is the key elegance of Archimedes' approach. Once you know the buoyant force and the fluid density, you can compute the displaced volume, which equals the object's volume when fully submerged. Dividing the object's mass by that volume gives its density.
Any fluid with a known density works — just enter or select that density. Using a denser fluid (e.g. salt water or glycerin) increases the buoyant force for the same object, making the difference in readings larger and easier to measure accurately.
Also known as
TG we-Calculate Editorial Team. (2026). Buoyancy Experiment Calculator — Weight in Air vs Fluid [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/buoyancy-experiment-calculator
TG we-Calculate Editorial Team. "Buoyancy Experiment Calculator — Weight in Air vs Fluid." TG we-Calculate. 2026. https://we-calculate.com/calculator/buoyancy-experiment-calculator.
TG we-Calculate Editorial Team, "Buoyancy Experiment Calculator — Weight in Air vs Fluid," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/buoyancy-experiment-calculator
@misc{wecalculate_buoyancy_experiment_calculator, title = {Buoyancy Experiment Calculator — Weight in Air vs Fluid}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/buoyancy-experiment-calculator}}, year = {2026}, note = {TG we-Calculate} }
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