You can compare the sizes of two balls by measuring either their diameter or their volume and then comparing those numbers.

1. Fast, practical answer (diameter)

If you just need to know which ball is bigger and by how much, measure the diameter of each ball (the distance straight across through the center):

  1. Place the ball against a wall or between two flat objects (like books) so they just touch the sides of the ball.
  2. Measure the distance between the two flat surfaces with a ruler or tape measure – that’s the diameter.
  3. Do the same for the second ball.
  4. Compare the two diameters: the one with the larger diameter is the bigger ball.

If you only have a tape measure or string:

  1. Wrap the tape/string around the widest part of each ball to get the circumference.
  2. Convert to diameter with the formula

d=Cπd=\frac{C}{\pi}d=πC​

where CCC is circumference and π≈3.14\pi \approx 3.14π≈3.14.

  1. Compare the diameters.

2. More “scientific” answer (volume)

If you want to compare how much space each ball takes up:

  1. Measure the diameter of each ball as above.
  2. Find the radius by dividing each diameter by 2.
  3. Use the sphere volume formula:

V=43πr3V=\frac{4}{3}\pi r^3V=34​πr3

  1. Calculate volume for each ball and compare.
    • Larger volume ⇒ bigger ball in terms of space it occupies.

Example:

  • Ball A radius: 5 cm → VA=43π(53)V_A=\frac{4}{3}\pi (5^3)VA​=34​π(53).
  • Ball B radius: 6 cm → VB=43π(63)V_B=\frac{4}{3}\pi (6^3)VB​=34​π(63) (clearly larger).

3. Very simple “no math” comparison

If you don’t need exact numbers:

  • Put both balls side by side and look at which is wider.
  • Roll one in front of the other and see which “sticks out” more on the sides.
  • Place each in a box or against a corner and mark the height – the one that reaches higher is larger.

4. If the balls aren’t perfect spheres

If they’re squishy or not exactly round:

  • Take several diameter measurements at different angles (up-down, left-right, diagonal).
  • Average those measurements for each ball, then compare the averages.

5. HTML summary table

Here’s a quick HTML table summarizing methods:

html

<table>
  <thead>
    <tr>
      <th>Method</th>
      <th>What you measure</th>
      <th>Tools needed</th>
      <th>What you can compare</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Direct diameter</td>
      <td>Distance across the ball</td>
      <td>Ruler, tape, or caliper</td>
      <td>Which ball has the larger diameter</td>
    </tr>
    <tr>
      <td>Circumference to diameter</td>
      <td>Distance around the ball</td>
      <td>Flexible tape or string</td>
      <td>Diameters using d = C / π</td>
    </tr>
    <tr>
      <td>Volume (using radius)</td>
      <td>Radius, then compute volume</td>
      <td>Ruler + calculator</td>
      <td>Which occupies more space (volume)</td>
    </tr>
    <tr>
      <td>Water displacement</td>
      <td>Volume of water displaced</td>
      <td>Graduated container, water</td>
      <td>Compare volumes directly</td>
    </tr>
    <tr>
      <td>Visual/height check</td>
      <td>Relative height or width</td>
      <td>Eyes, maybe a wall/mark</td>
      <td>Rough “which is bigger”</td>
    </tr>
  </tbody>
</table>

TL;DR: The cleanest answer to “how would you measure and compare the sizes of the two balls?” is:

Measure the diameter of each ball (directly or via circumference) and compare those diameters; if needed, use the sphere volume formula with their radii to compare how much space each ball occupies.