Radius and Diameter worksheet - Free Printable

Let’s go through each circle one by one. Remember:

- The circle is named by the point in the center.
- A radius goes from the center to the edge (any line like that).
- A diameter goes all the way across, passing through the center, with both ends on the edge.

---

Top Right Circle:

Center point = R → so circle is R

Radius: any line from R to edge → RB or RI or RD → pick one, say RB

Diameter: must pass through R and have both ends on edge → DI passes through R? Yes! D to I goes through R → DI

Wait — let’s check: points are B, I, D. Center is R. Line from D to I passes through R? Looking at diagram — yes, it’s a straight line through center. So diameter is DI

But wait — sometimes they write it as ID or DI — either is fine. Let’s use DI

Actually, looking again — the line from D to I does go through R. So yes.

So:
- circle: R
- radius: RB (or RI or RD)
- diameter: DI

But let’s be consistent — maybe pick RB for radius since it’s drawn clearly.

Actually, in the first example, they used FO and RG — so they picked specific ones. We can pick any correct ones.

Let me double-check: In top right, points are B, I, D on edge, R in center. Lines drawn: RB, RI, RD, and DI (which is diameter).

So:
- circle: R
- radius: RB (example)
- diameter: DI

But actually, DI is not labeled as a single segment? Wait — in the diagram, there’s a line from D to I passing through R — yes, that’s the diameter.

Okay.

---

Middle Left Circle:

Points: T, O, A on edge; G in center.

Lines: TO (horizontal), GA (vertical) — both pass through G.

TO goes from T to O through G → that’s diameter.

GA goes from G to A → radius.

Also, GT and GO are radii too.

So:
- circle: G (center)
- radius: GA (or GT or GO)
- diameter: TO

Yes.

---

Middle Right Circle:

Points: M, A, B on edge; L in center.

Lines: LM, LA, LB — all radii.

MB? Does MB pass through L? Looking — M to B is a straight line through L? Yes — because L is center, and M and B are opposite? Actually, in diagram, M to B is drawn as a straight line through L — so that’s diameter.

A is another point — LA is radius.

So:
- circle: L
- radius: LA (or LM or LB)
- diameter: MB

Yes.

---

Bottom Left Circle:

Points: A, T, S on edge; C in center.

Lines: CA, CT, CS — radii.

AS? From A to S — passes through C? Yes — vertical line through center → diameter.

T is another point — CT is radius.

So:
- circle: C
- radius: CT (or CA or CS)
- diameter: AS

Yes.

---

Bottom Right Circle:

Points: S, O, G on edge; D in center.

Lines: DS, DO, DG — radii.

SG? From S to G — passes through D? Yes — horizontal line through center → diameter.

O is another point — DO is radius.

So:
- circle: D
- radius: DO (or DS or DG)
- diameter: SG

Yes.

---

Now let’s write them all neatly.

Final Answer:

Top Right:
- circle: R
- radius: RB
- diameter: DI

Middle Left:
- circle: G
- radius: GA
- diameter: TO

Middle Right:
- circle: L
- radius: LA
- diameter: MB

Bottom Left:
- circle: C
- radius: CT
- diameter: AS

Bottom Right:
- circle: D
- radius: DO
- diameter: SG

Wait — in the first example, they wrote “FO” and “RG” — which are two-letter names. So we should do same.

Also, for diameter, in first example, RG — but R and G are both on edge, and F is center — so RG passes through F? In first diagram: points R, G, O on edge, F center. Line from R to G — does it pass through F? Looking — yes, because F is connected to R and G, and R-F-G is straight? Actually, in first diagram, R to G is not directly drawn — wait no, in first diagram, they have lines FR, FG, FO — and then they say diameter is RG — meaning the line from R to G passing through F.

In the diagram, R and G are on opposite sides? Actually, in first circle: points R, G, O. Center F. They drew FR, FG, FO. Then they said diameter is RG — which implies that R and G are endpoints of a diameter, so line RG passes through F.

Similarly, in our answers, we need to make sure the diameter we pick actually passes through center.

In top right: D to I — does it pass through R? Yes, as per diagram.

In middle left: T to O — passes through G? Yes.

In middle right: M to B — passes through L? Yes.

In bottom left: A to S — passes through C? Yes.

In bottom right: S to G — passes through D? Yes.

All good.

For radius, any one is fine — I’ll pick the ones that are drawn or obvious.

In top right, RB is drawn — so RB.

In middle left, GA is drawn — so GA.

In middle right, LA is drawn — so LA.

In bottom left, CT is drawn — so CT.

In bottom right, DO is drawn — so DO.

Perfect.

Final Answer:

Top Right:
circle: R
radius: RB
diameter: DI

Middle Left:
circle: G
radius: GA
diameter: TO

Middle Right:
circle: L
radius: LA
diameter: MB

Bottom Left:
circle: C
radius: CT
diameter: AS

Bottom Right:
circle: D
radius: DO
diameter: SG