Will It Float? Density Calculator
Enter a mass and a volume to get the density, then drop your object into a fluid and see how much of it stays above the surface. Every number comes from the formulas below, and the math is shown with each result.
- Result
- Below the surface
- Above the surface
- Density
- In kg/m³
- In lb/ft³
- Fluid density
- The arithmetic
How to calculate density
Density tells you how much mass is packed into each bit of space. The formula has one step:
density = mass ÷ volume
Here is a worked example. A block has a mass of 340 g and a volume of 500 cm³.
- Divide: 340 g ÷ 500 cm³ = 0.68 g/cm³.
- Convert to kg/m³ by multiplying by 1,000: 680 kg/m³.
- Convert to lb/ft³ by multiplying by about 62.43: about 42.45 lb/ft³.
- Compare with fresh water at 70°F: 0.68 ÷ 0.99802 ≈ 0.681. That is below 1, so the block floats with about 68.1% below the surface and 31.9% above it.
US units work the same way, as long as you convert before you compare. Ten ounces in 20 cubic inches is 283.5 g ÷ 327.7 cm³, or about 0.865 g/cm³. The calculator uses the standard conversions: 1 lb = 453.59237 g, 1 oz = 28.349523125 g and 1 in = 2.54 cm, which agree with the rounded factors published by NIST.
Why things float
A fluid pushes up on anything sitting in it. That push, the buoyant force, equals the weight of the fluid the object moves out of the way. A floating object settles at the depth where that push matches its own weight. A physics textbook from OpenStax boils the result down to a comparison: an object whose average density is lower than the fluid's will float, and one that is denser will sink.
The same comparison tells you how deep a floater rides:
fraction below the surface = object density ÷ fluid density
For ice in fresh water at 32°F, that is 0.9167 ÷ 0.99987 ≈ 0.917, or about 91.7% below the surface. If you want the full story of why ice is less dense in the first place, read why ice floats. If the ratio is above 1, the object sinks. The tank in the tool draws its block so that the share of its height under the surface equals the computed fraction once it stops moving.
Densities used in this tool
Density changes with temperature, so each value below comes with the condition its source lists. All values are in g/cm³.
| Material | g/cm³ | Condition | Ref. |
|---|---|---|---|
| Ice | 0.9167 | 32°F (0°C) | [2] |
| Cork | 0.240 | 32°F (0°C) | [4] |
| Pine wood | 0.373 | 32°F (0°C) | [4] |
| Oak wood | 0.710 | 32°F (0°C) | [4] |
| Aluminum | 2.70 | 32°F (0°C) | [4] |
| Iron | 7.86 | 32°F (0°C) | [4] |
| Copper | 8.92 | 32°F (0°C) | [4] |
| Lead | 11.3 | 32°F (0°C) | [4] |
| Gold | 19.3 | 32°F (0°C) | [4] |
| Fresh water | 0.99987 | 32°F (0°C) | [1] |
| Fresh water | 0.99802 | 70°F (21°C) | [1] |
| Seawater | 1.027 | 32°F (0°C), 3.5% salinity | [3] |
| Olive oil | 0.920 | 32°F (0°C) | [4] |
| Ethyl alcohol | 0.806 | 32°F (0°C) | [4] |
| Glycerin | 1.26 | 32°F (0°C) | [4] |
| Mercury | 13.6 | 32°F (0°C) | [4] |
Sources do not always match to the last digit. OpenStax lists seawater at 1.030 g/cm³ at 32°F, a little above the 1.027 used here. NIST's table of elements gives iron as 7.874 and gold as 19.32, close to the rounded textbook values, though that table does not state a temperature. None of these gaps changes whether those materials float or sink in the fluids here.
What this model leaves out
This is an idealized calculator, so treat its answer as a clear estimate and not as a measurement of the thing on your desk.
- A uniform object. It assumes the same density all the way through. Real wood varies a lot: Penn State Extension describes large differences between species and notes that density changes as wood dries.
- No trapped air. What counts is average density, so shape matters. OpenStax explains that steel ships float for this reason, even though a solid lump of steel sinks. Enter a hollow object's total mass and its total outer volume to get its average density.
- No surface tension. The USGS points out that a steel paper clip or needle, placed carefully, can rest on water even though steel is much denser. The formula here predicts a sink, because it ignores this effect.
- Still fluid at one temperature. Nothing dissolves, soaks in, melts or mixes, and the listed fluid density stays fixed. Close calls can go either way in real life. Ice in olive oil comes out at about 99.6% below the surface, which is too near the line to trust.
- A cartoon tank. Only the object's depth is to scale. The tank's size and the water level are for show.
Mercury is on the list only as a number to compare. The EPA warns that breathing its vapor can harm your health, so please never try that one at home.
Dr. Pippa is a cartoon host, and her speech bubbles are jokes. The results panel holds the actual numbers. You can find more tools in the Science Lab.
References
- Water Density. U.S. Geological Survey, Water Science School.
- Density of Ice. Physics Van, University of Illinois.
- Some useful facts about water and ice. Food and Agriculture Organization of the United Nations.
- 14.1 Fluids, Density, and Pressure, University Physics Volume 1. OpenStax, Rice University.
- 14.4 Archimedes' Principle and Buoyancy, University Physics Volume 1. OpenStax, Rice University.
- Table 1: Material constants for elemental media. National Institute of Standards and Technology.
- NIST Guide to the SI, Appendix B: Conversion Factors. National Institute of Standards and Technology.
- Surface Tension and Water. U.S. Geological Survey, Water Science School.
- Calculating the Green Weight of Wood Species. Penn State Extension.
- Health Effects of Exposures to Mercury. U.S. Environmental Protection Agency.