Formula used
Specific gravity is a dimensionless ratio between a material’s bulk density and a reference fluid density:
- SG = ρbulk / ρref
- ρbulk is the bulk density of the material.
- ρref is the reference density (commonly water at a stated temperature).
How to use this calculator
- Enter your bulk density value from lab or field measurements.
- Select the unit that matches your measurement report.
- Pick a reference density preset, or choose a custom value.
- Set decimal places and optional scientific notation for readability.
- Press Calculate to view results above the form.
- Use the CSV/PDF buttons to save a clean report.
Example data table
| Material | Bulk density | Unit | Reference | ρref (kg/m³) | Specific gravity |
|---|---|---|---|---|---|
| Dry sand | 1600 | kg/m³ | Water (20°C) | 998.2 | 1.6029 |
| Portland cement (bulk) | 94 | lb/ft³ | Water (4°C) | 1000 | 1.5057 |
| Polymer pellets | 0.62 | g/cm³ | Water (25°C) | 997.05 | 0.6218 |
| Salt solution (material bulk) | 1200 | kg/m³ | Custom reference | 1025 | 1.1707 |
Examples are illustrative. Always match the reference density to your standard.
Bulk density and specific gravity guide
1) What the calculator measures
Bulk density is mass per total volume, including voids between particles. Specific gravity is the ratio of that bulk density to a chosen reference density. Because it is a ratio, specific gravity has no units and is easy to compare across reports and measurement systems.
2) Why reference density matters
Many standards use water as the reference, but water density changes with temperature. Typical values include 1000 kg/m³ at 4°C, about 998.2 kg/m³ at 20°C, and about 997.05 kg/m³ at 25°C. Selecting the same reference keeps results consistent across labs.
3) Typical bulk density ranges
Dry sand often falls near 1500–1700 kg/m³, while cement powder commonly ranges around 1100–1500 kg/m³ depending on aeration and handling. Polymer pellets can be much lower, sometimes 500–700 kg/m³. These ranges help you sanity-check inputs before exporting reports.
4) Unit conversions used in practice
Engineering reports frequently mix units. This tool converts common inputs such as g/cm³ and lb/ft³ into kg/m³ for the core calculation. A useful reference: 1 g/cm³ equals 1000 kg/m³. Another: 1 lb/ft³ equals 16.018463 kg/m³, which is common in bulk solids specifications.
5) Interpreting specific gravity values
If SG is 1.60 (with water as reference), the bulk density is roughly 60% greater than water. SG below 1.0 indicates the bulk density is lower than the reference. This interpretation supports quick screening for storage design, mix batching, and transport documentation.
6) Moisture, compaction, and sampling effects
Bulk density can shift noticeably with moisture content, particle size distribution, vibration, and compaction method. A lightly poured sample may read lower than a tapped or compacted sample by several percent. Record the test method so the calculated specific gravity aligns with your process conditions and QA checks.
7) Using custom reference densities
Some workflows compare materials to brine, oils, or slurries rather than water. A typical seawater density is near 1025 kg/m³, though it varies with salinity and temperature. Entering a custom reference lets you compute SG for specialized flotation, separation, and pipeline applications.
8) Reporting and exporting results
After calculation, the results appear above the form for quick review. The CSV export captures inputs, reference density, and converted bulk densities. The PDF export creates a clean one-page summary for lab notebooks, QA attachments, and shipping records where a consistent format reduces manual transcription errors.
FAQs
1) Is specific gravity the same as density?
No. Density has units and depends on measurement units. Specific gravity is a unitless ratio of bulk density to a reference density, usually water at a stated temperature.
2) What reference density should I choose?
Use the reference specified by your standard or report. Water at 4°C is 1000 kg/m³, while water near 20°C is about 998.2 kg/m³. Consistency matters more than the exact choice.
3) Can I use this for powders and granules?
Yes. Bulk density is commonly reported for powders, pellets, aggregates, and grains. Make sure your bulk density test method is documented, because pouring, tapping, and compaction can change the value.
4) Why does my SG change after drying the sample?
Moisture adds mass and can change packing behavior. When the sample dries, both mass and void structure may change, shifting bulk density and therefore the specific gravity ratio for the selected reference.
5) What if my input is in lb/ft³?
Select lb/ft³ as the unit. The calculator converts it internally using 1 lb/ft³ = 16.018463 kg/m³, then computes specific gravity and displays converted densities for easy comparison.
6) How many decimals should I display?
Match your measurement precision. Many lab reports use 3–4 decimals for specific gravity, while bulk density may need fewer. The decimal setting also controls rounding in the CSV and PDF exports.
7) When should I use a custom reference density?
Use it when your workflow compares to fluids other than water, like seawater, brines, or oils. Enter the reference density in kg/m³ so the ratio matches your application and documentation.