how to find density

June 27, 2026

Density tells you how much mass there is in a certain amount of space (volume). It’s found with a very simple formula:

density=massvolume\text{density}=\frac{\text{mass}}{\text{volume}}density=volumemass

Quick Scoop: The Core Idea

Formula: ρ=mV\rho =\frac{m}{V}ρ=Vm
- ρ\rho ρ: density
- mmm: mass
- VVV: volume
Typical units:
- Solids/liquids: g/cm³ or kg/m³
- Gases: kg/m³ is common

Example: If a metal block has a mass of 200 g and a volume of 50 cm³,

ρ=200textg50textcm3=4textg/cm3\rho =\frac{200\\text{g}}{50\\text{cm}^3}=4\\text{g/cm}^3ρ=50textcm3200textg=4textg/cm3

Step‑by‑Step: How to Find Density

Measure the mass
- Use a balance or scale.
- Record in grams (g) or kilograms (kg).
Find the volume
- Regular solid (cube, rectangular block, cylinder):
  - Cube/block: V=length×width×heightV=\text{length}\times \text{width}\times \text{height}V=length×width×height.
  - Cylinder: V=πr2hV=\pi r^2hV=πr2h.
- Liquid:
  - Pour into a measuring cylinder or beaker and read off the volume (mL or cm³).
- Irregular solid (weird shape):
  - Use water displacement :
    - Fill a graduated cylinder with water and note the initial volume.
    - Gently lower the object in.
    - Note the new volume.
    - Volume of object = new volume − initial volume.
Calculate density
- Plug into ρ=mV\rho =\frac{m}{V}ρ=Vm.
- Make sure mass and volume are in compatible units (e.g., g and cm³, or kg and m³).

Example Problems

Example 1: Regular Solid

A small brick has:

Mass = 600 g
Dimensions = 10 cm × 5 cm × 2 cm

Volume:

V=10×5×2=100textcm3V=10\times 5\times 2=100\\text{cm}^3V=10×5×2=100textcm3

Density:

ρ=600textg100textcm3=6textg/cm3\rho =\frac{600\\text{g}}{100\\text{cm}^3}=6\\text{g/cm}^3ρ=100textcm3600textg=6textg/cm3

Example 2: Liquid

You have some oil in a measuring cylinder:

Volume = 250 mL (= 250 cm³)
Mass of cylinder + oil = 340 g
Mass of empty cylinder = 90 g

Mass of oil:

m=340−90=250textgm=340-90=250\\text{g}m=340−90=250textg

Density:

ρ=250textg250textcm3=1textg/cm3\rho =\frac{250\\text{g}}{250\\text{cm}^3}=1\\text{g/cm}^3ρ=250textcm3250textg=1textg/cm3

Example 3: Irregular Object (Water Displacement)

A small rock:

Mass = 45 g
Initial water level in cylinder = 30 mL
Final water level with rock = 42 mL

Volume of rock:

V=42−30=12textcm3V=42-30=12\\text{cm}^3V=42−30=12textcm3

Density:

ρ=45textg12textcm3≈3.75textg/cm3\rho =\frac{45\\text{g}}{12\\text{cm}^3}\approx 3.75\\text{g/cm}^3ρ=12textcm345textg≈3.75textg/cm3

Handy HTML Table (for your post)

Here’s an HTML table you can drop directly into your content:

html

<table>
  <thead>
    <tr>
      <th>Type of material</th>
      <th>How to measure mass</th>
      <th>How to measure volume</th>
      <th>Density formula use</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Regular solid (cube, block)</td>
      <td>Scale or balance</td>
      <td>Use dimensions (L × W × H)</td>
      <td>Density = mass ÷ volume</td>
    </tr>
    <tr>
      <td>Liquid</td>
      <td>Weigh container full − empty container</td>
      <td>Read volume in measuring cylinder</td>
      <td>Density = mass ÷ volume</td>
    </tr>
    <tr>
      <td>Irregular solid (rock, key)</td>
      <td>Scale or balance</td>
      <td>Water displacement (final − initial level)</td>
      <td>Density = mass ÷ displaced volume</td>
    </tr>
  </tbody>
</table>

Mini FAQ

Q: What is density in simple words?
A: How tightly packed the matter is in something.
Q: Why is density useful?
- Helps identify substances.
- Explains floating or sinking (less dense than water → floats, more dense → sinks).
Q: Can I find mass or volume if I know density?
- Yes:
  - m=ρ×Vm=\rho \times Vm=ρ×V
  - V=mρV=\frac{m}{\rho}V=ρm

TL;DR

To find density, measure mass, measure volume, then divide:

density=massvolume\text{density}=\frac{\text{mass}}{\text{volume}}density=volumemass