How to Measure Solid Density with a Density Balance

What "measure density" actually means

Density is mass divided by volume. A density balance does not measure volume directly — it measures the mass of a sample twice: once in air, once while the sample is suspended in a liquid of known density. The difference between those two masses is the buoyant force, which (by Archimedes' principle) equals the weight of the liquid the sample displaces. From that, the instrument recovers the volume and divides mass by volume to give you density. On an integrated density meter the whole calculation is done for you and the result appears on the display.

1. Archimedes' principle, in plain terms

When an object is immersed in a liquid it pushes liquid out of the way. The liquid pushes back with a force equal to the weight of the displaced liquid. A solid denser than water sinks, and the reading in the liquid is lighter than in air by exactly that displaced weight. Because the liquid's density is known, the displaced volume is known, and density = mass ÷ volume follows directly. The reference liquid is usually water (density ≈ 1.000 g/cm³), but the meter can use other auxiliary liquids whose density you enter into the instrument.

2. Two ways to do it: density kit vs integrated meter

You can reach an Archimedes measurement two ways. The first is to hang a density kit on an ordinary analytical or precision balance: you weigh the sample in air, weigh it suspended in a beaker of liquid, and let the balance's density function compute the result. The second is an integrated density meter, where the density determination set lives inside the weighing chamber and the display reads density directly.

The integrated route has one big advantage: the suspension geometry is fixed by design, so the result does not depend on how carefully each operator rigged the kit. That consistency is why a multi-operator QC bench or a teaching lab tends to prefer a purpose-built meter over a clip-on kit on a shared balance.

3. Measuring a regular solid, step by step

1. Prepare the reference liquid. Fill the suspension vessel with the chosen liquid. If you use water, the meter already knows its density; if you use another liquid, enter its value and the adjustable temperature-compensation coefficient so the density stays correct across the room's temperature range.
2. Zero and weigh in air. Hang the sample from the wire and read its dry mass. Make sure the sample is clean, dry and free of surface moisture.
3. Immerse and suspend. Lower the sample fully into the liquid, completely submerged, without touching the vessel walls or the bottom. Tap gently to release any trapped air bubbles — a single bubble is enough to throw the result off.
4. Read the density. The display shows density directly in g/cm³. No arithmetic, no lookup table.

4. Readability: how fine can you read?

Density resolution follows the balance's weighing readability. On the MD series the four models split into three resolution classes:

5. Capacity and the hanging pan

The four models cover 120 g, 200 g, 300 g and 3000 g. Note the hanging-pan size changes with the class: Ø 60 mm on the finest MD-124, Ø 160 mm on the MD-200, MD-300 and MD-3000. Weigh your largest real sample together with its holder or suspension wire before you choose — a part that overhangs the pan defeats the measurement.

6. When you need an extra kit

• Regular solids of any shape are handled by the standard suspension (pure-water displacement) method.
• Floating samples — parts less dense than the reference liquid will not stay submerged on their own. An optional floating-sample determination kit holds them under.
• Granules and pellets cannot be weighed as one immersed body; an optional granule determination kit measures them reproducibly.

7. Mistakes that quietly ruin the result

• Air bubbles clinging to the sample or the wire — the single most common error.
• The sample touching the vessel wall or bottom, which adds stray support force.
• The wrong reference-liquid density entered, or forgetting that it drifts with temperature.
• Overloading beyond the model's capacity or hanging-pan size.
• Surface moisture on a "dry" sample that should be weighed in air.

8. Records and traceability

For any documented workflow, an RS-232C interface connects a printer or a PC so each density result is saved with its method. A backlit LCD keeps the reading clear, and tare / zero / overload indication runs across the whole weighing range — useful when you switch between samples and holders all day.

9. Quick measurement checklist

• Smallest density difference you must resolve? → sets the resolution class (0.0001 / 0.001 / 0.01 g/cm³).
• Heaviest sample plus holder? → sets capacity and pan size.
• Does anything float or arrive as granules? → order the optional kits.
• Is the reference liquid water, or something else? → enter its density and temperature coefficient.
• Do you need saved records? → confirm the RS-232C connection.

Our MD series density meter at a glance

The MD series solid density meter is an integrated Archimedes-principle instrument: the density determination set sits inside the weighing chamber and the density result is read directly. Four models cover 120 g / 200 g / 300 g / 3000 g, with weighing readability from 0.0001 g (MD-124) to 0.01 g (MD-3000) and density resolution down to 0.0001 g/cm³. The pure-water displacement (suspension) method is standard; the density of other auxiliary liquids can be set and the temperature-compensation coefficient is adjustable. Optional kits extend measurement to floating samples and granules. A backlit LCD, tare / zero / overload indication and a standard RS-232C interface make it a practical density testing balance for quality control and education.

Related product: MD Series Density Meter