Specific Gravity Change Calculator

Enter readings

Input type

Choose SG readings or density values.

Density unit

Used only for density input.

Reference temperature (°C)

Common choices: 15, 20, or 25 °C.

Initial reading

Enter SG (unitless) or density.

Final reading

Enter SG (unitless) or density.

Material / fluid (optional)

Included in downloads.

Initial temperature (°C)

Temperature when initial reading was taken.

Final temperature (°C)

Temperature when final reading was taken.

Notes (optional)

Reset

Example data table

Scenario	Input type	Initial	Final	Ref Temp	ΔSG (ref)	% Change
Brine adjustment	SG	1.070 @ 24°C	1.082 @ 24°C	20°C	+0.0119	+1.11%
Coolant dilution	Density	1045 kg/m³ @ 25°C	1030 kg/m³ @ 25°C	20°C	-0.0150	-1.43%
Syrup batch check	SG	1.210 @ 30°C	1.205 @ 30°C	20°C	-0.0049	-0.41%
Process stability	Density	998.5 kg/m³ @ 19°C	999.2 kg/m³ @ 19°C	20°C	+0.0007	+0.07%

Examples are illustrative, not a laboratory specification.

Formula used

1) Specific gravity definition

Specific gravity is a ratio of sample density to water density: SG = ρ_sample / ρ_water.

Here, water density depends on temperature, so the reference temperature matters.

2) Converting an SG reading to a reference temperature

If your SG was measured relative to water at the measurement temperature: SG_ref = SG_meas × ρ_w(T_meas) / ρ_w(T_ref).

This aligns SG readings to a consistent water reference.

3) Using density directly

If you enter absolute density: SG_ref = ρ_sample / ρ_w(T_ref).

Density units are converted to kg/m³ internally.

4) Change metrics

ΔSG = SG_final,ref − SG_initial,ref

% Change = (ΔSG / SG_initial,ref) × 100

How to use this calculator

Select whether your readings are SG or density.
Enter the reference temperature for reporting.
Fill initial and final readings and their temperatures.
Click Calculate to view corrected SG and changes.
Use the download buttons to export your results.

Specific gravity change guide

1) What specific gravity change tells you

Specific gravity (SG) tracks how concentrated a liquid is compared with water. A change of just 0.010 can be meaningful: for brines and coolants it often indicates a concentration shift near 1–2% by mass, depending on the solute. Use this calculator to compare two readings on the same reference basis.

2) Temperature correction matters

Water density varies with temperature, so the same liquid can show different SG values when measured warm versus cool. Standard reporting temperatures are commonly 15 °C, 20 °C, or 25 °C. By converting both readings to one reference temperature, you isolate real process changes from temperature-driven measurement differences.

3) Water density reference data

Around room temperature, water density is close to 998–1000 kg/m³. Typical reference points are about 999.1 kg/m³ at 15 °C, 998.2 kg/m³ at 20 °C, and 997.0 kg/m³ at 25 °C. Small changes in these values slightly shift SG when you standardize to a reference temperature.

4) Reading the delta and percent change

The calculator reports ΔSG and percent change. If SG rises from 1.070 to 1.082 at the same reference, ΔSG is +0.012 and percent change is about +1.12%. In quality control, you can set alert limits (for example, ±0.003 SG) to catch drift early.

5) SG input versus density input

Use SG input when you read from a hydrometer or digital densitometer reporting SG directly. Use density input when your lab instrument reports absolute density (kg/m³, g/mL, or lb/ft³). The calculator converts density to SG at the selected reference temperature, so results are comparable across instruments.

6) Typical ranges you may encounter

Many petroleum products fall near 0.70–0.95 SG, water-based solutions often sit near 0.98–1.10, and heavy brines can be 1.10–1.30 or higher. Food syrups may exceed 1.20. Comparing changes within a product’s normal band is often more useful than comparing across unrelated fluids.

7) Sampling and measurement tips

Take samples consistently: same tank depth, same mixing time, and clean glassware. Let bubbles dissipate and record the measurement temperature. For routine checks, repeat the reading twice and watch the spread; if two readings differ by more than 0.001 SG, re-sample or verify calibration.

8) Reporting and documentation

Exporting CSV helps build trends across time, batches, or shifts. PDF is useful for audits and sign-offs, especially when you include sample IDs and notes. Store reference temperature, instrument type, and operator name to make comparisons reproducible and reduce confusion when values are reviewed later.

FAQs

1) Is SG the same as density?

SG is a ratio, so it has no units. Density is mass per volume (like kg/m³). SG depends on the water reference density, which changes with temperature.

2) Why choose a reference temperature?

A reference temperature makes readings comparable. If you measure at different temperatures, water density changes and SG shifts. Converting to one reference reduces false “changes.”

3) Which reference temperature should I use?

Use the standard used by your industry or lab, commonly 15 °C, 20 °C, or 25 °C. The best choice is the one used for your historical records.

4) Can I compare SG readings from different instruments?

Yes, if both readings are corrected to the same reference temperature and taken on comparable samples. Record instrument type and calibration date to support traceability.

5) What does a negative ΔSG mean?

A negative ΔSG means the final corrected SG is lower than the initial corrected SG. This often indicates dilution, temperature-related measurement differences, or a composition change.

6) How accurate are the water density values?

The calculator uses a standard engineering approximation for water density versus temperature. It is suitable for process monitoring and reporting, but it is not a substitute for certified laboratory methods.

7) What if my initial SG is zero?

Percent change is not defined when the initial value is zero, so the calculator omits it. Use ΔSG and the final value for interpretation in that case.