Calculator Inputs
Choose one method. Fill the fields used by that method. Extra fields may stay blank.
Formula Used
Direct ratio: SG = Wsample / Wwater(equal volume)
Buoyancy method: SG = Wair / (Wair - Wsubmerged)
Weight-volume method: SG = Wsample / (g × V × ρreference)
Specific gravity compares sample density with a reference fluid density. It has no unit. Weight can be force or a mass reading from a scale. The calculator converts selected units before applying the chosen formula.
How to Use This Calculator
- Select the method that matches your measurements.
- Enter the sample weight in air and choose its unit.
- Enter equal-volume water weight, submerged weight, or volume as needed.
- Choose the reference density preset or enter a custom value.
- Adjust local gravity and decimal places if needed.
- Press the calculate button and read the result above the form.
- Use the CSV or PDF buttons to save the result.
Example Data Table
| Method | Sample weight | Second measurement | Reference density | Expected SG |
|---|---|---|---|---|
| Direct ratio | 98.0665 N | 39.2266 N water weight | 998.207 kg/m³ | 2.5000 |
| Buoyancy | 10 kgf | 6 kgf submerged | 1000 kg/m³ | 2.5000 |
| Weight-volume | 98.0665 N | 400 mL volume | 1000 kg/m³ | 2.5000 |
Understanding Specific Gravity by Weight
Specific gravity is a ratio. It compares a sample with a reference fluid. In most school and lab work, the reference is water. The value has no unit. A result of 2.50 means the sample is two and one half times as dense as water.
Weight methods are useful when scales are easier than density instruments. A balance can measure weight in air. The same object can also be weighed while submerged. The loss of weight equals buoyant force. That force matches the weight of displaced water. This idea comes from Archimedes principle.
Three Useful Weight Methods
The direct method is simple. Divide sample weight by the weight of equal volume water. Both weights must use the same unit. The unit cancels, so the result is specific gravity.
The submerged method uses apparent weight. First enter the true weight in air. Then enter the apparent weight while fully under water. Subtract the submerged reading from the air reading. This gives the water displacement weight. Divide the air weight by that difference.
The volume method uses weight and measured volume. The calculator converts weight to mass with local gravity. It then divides mass by volume. That sample density is divided by reference water density.
Why Reference Density Matters
Water density changes with temperature. Pure water near 4°C is about 1000 kg per cubic meter. At room temperature it is slightly lower. For many rough checks the difference is small. For careful work, choose the closest reference setting. You may also enter a custom density.
Local gravity also matters when weight is treated as force. Most classroom work uses 9.80665 meters per second squared. Field measurements can use a local value. This improves density from weight and volume.
Good Measurement Practice
Use clean samples. Remove trapped bubbles before submerged weighing. Bubbles reduce apparent weight loss. That makes specific gravity look too high. Dry porous materials before direct weighing, unless wet density is required.
Use matching units for paired weights. Do not mix pound force with gram force without conversion. This calculator accepts many force and mass equivalent units. It converts them before calculation.
When This Calculator Helps
The tool supports minerals, metals, plastics, soils, liquids, and lab samples. It can help compare quality, purity, or material identity. It also supports field checks when a full density setup is not available.
Specific gravity is not enough for every decision. Temperature, porosity, dissolved salts, and surface coatings can change the reading. Use the result as a strong physics estimate. Confirm critical materials with calibrated laboratory methods.
Interpreting Results
A value below one means the sample is lighter than water. It may float if surface forces and shape allow it. A value near one suggests similar density. Large values often point to metals, dense minerals, or concentrated solutions. Always record the method, units, temperature, and reference density beside the final number.
FAQs
What is specific gravity?
Specific gravity is the ratio of a sample density to a reference density. Water is usually the reference. The value has no unit because both densities cancel during division.
How can weight give specific gravity?
Weight is proportional to mass. If two equal volumes are compared under the same gravity, the weight ratio equals the density ratio. That ratio is the specific gravity.
Which method should I choose?
Use direct ratio when you know sample weight and equal-volume water weight. Use buoyancy when you have air and submerged weights. Use volume method when you know sample weight and volume.
Why does the submerged method work?
A submerged object loses apparent weight because water pushes upward. That loss equals the weight of displaced water. Dividing air weight by this loss gives specific gravity.
Does specific gravity have a unit?
No. Specific gravity is a ratio. It compares two densities or two equivalent weights. Since matching units divide out, the final number is dimensionless.
Why include local gravity?
Local gravity matters when weight is converted into mass for the volume method. Direct weight ratios are less sensitive because the same gravity affects both weights.
Can I use mass readings instead of force?
Yes. Select a mass reading unit, such as kilograms, grams, or pounds. The calculator converts the reading using the local gravity value before calculating.
What reference density should I use?
Use water near your lab temperature for most work. Select 4°C, 20°C, or 25°C water. Choose custom density for brines, oils, or other reference fluids.
Can bubbles affect the result?
Yes. Bubbles add extra buoyancy during submerged weighing. This can make the apparent weight loss too large or unstable. Wet the sample carefully and remove trapped air.
Can this calculator check minerals?
Yes. Specific gravity is often used for minerals and metals. Clean the sample, measure carefully, and compare the result with trusted material data.
Is this suitable for critical testing?
It is suitable for learning, estimation, and field checks. For legal, safety, or commercial certification, use calibrated instruments and accepted laboratory procedures.