It is easiest to do this in a top view.
See below.

These are cross-sections of a cone with radius $3$ cm and a height of $3$ cm.

See the figure.

Using a top view you can measure or compute the width of each cross-section.
The first cross-section is a point.
The second cross-section has a width of $\sqrt{3^2-2^2}=\sqrt{5}$ cm and a height of $\frac{1}{3}\cdot 5=1\frac{2}{3}$ cm and the shape of a parabola.
The third cross-section has a width of $\sqrt{3^2-1^2}=\sqrt{8}$ cm and a height of $\frac{2}{3}\cdot 5=3\frac{1}{3}$ cm and also has the shape of a parabola.
The fourth cross-section is a isosceles triangle with a base of $6$ cm and a height of $5$ cm.
The fifth cross-section is equal to the third, The sixth is equal to the second and the seventh cross-section is a point again.

In a view you can calculate or measure he width of each cross-section.
The first cross-section is a point.
The second cross-section is a circle with radius $\sqrt{3^2-2^2}=\sqrt{5}$ cm.
The third cross-section is a circle with radius $\sqrt{3^2-1^2}=\sqrt{8}$ cm.
The fourth cross-section is a circle with radius $3$ cm.
The fifth cross-section is equal to the third, The sixth is equal to the second and the seventh cross-section is a point again.