SG Cup Calibration: How to Calibrate a Density Cup

By Robert Low, Director, Lead Auditor & BRCGS Approved Trainer

If you check the density or specific gravity of liquids with a density cup, the cup itself needs checking. My free SG cup calibration tool uses the density of water to work out a correction factor for your cup.

What the SG Cup Calibration Does

A density cup, or SG cup, is filled to a known volume and weighed. The weight tells you the density of the product. The catch is that the real volume of the cup is never exactly what is stamped on it, and that is why a correction factor matters.

You fill the cup with clean water at a measured temperature, weigh it, and compare the result with the known density of water at that temperature. The tool does the comparison and gives you the correction factor to apply to your product readings.

How to Use It

1. Open SG Cup Calibration on the free resources page.
2. Measure the water temperature and weigh the water in the cup.
3. Enter the values.
4. Record the correction factor against that cup, with the date and your initials.

Where It Helps Beyond Certification

Density feeds into more than a quality check. If you fill by weight but sell by volume, an error in density is an error in what the customer receives. That makes this a weights and measures issue as well as a quality one.

It is also straightforward calibration evidence. A dated record with a correction factor and the method used is exactly what an auditor wants to see for measuring equipment, and it takes five minutes.

Where Sites Get Caught Out

Temperature matters. Water density changes with temperature, so calibrate at a measured temperature and not at room temperature by assumption. Give each cup a unique ID so you do not mix up factors.

Related free tools: Weights & Measures checker.