Vernier calipers measure what?

• A. Length
• B. Width
• C. Radius
• D. Actual wire diameter

Answer: (D)

Vernier calipers provide a precise external measurement by reading the distance between the outside jaws. When you place a round wire between those jaws, the measurement shown is the wire’s diameter—the actual cross‑sectional size of the wire. While you could use calipers to assess length or other dimensions in different contexts, the direct, read‑off value for a round wire is its diameter, not the radius (which would require halving the reading) or a generic length/width. So the best answer is the actual wire diameter.