Digital calipers sound like a machinist's tool. On a commercial electrical job they're a diagnostic and verification instrument you'll reach for more often than you'd expect.
What You're Measuring
Conduit OD when you need the right fitting and you don't have the original spec. Knockout punch sizing when you're matching to existing work. Conductor diameter when you're sourcing a replacement and the label's worn off. Box fill calculations that require knowing actual conductor dimensions. These come up. A caliper gives you the number in seconds.
Digital Caliper 6" — inside, outside, depth. Field-accurate to 0.01mm.
View on Amazon ↗Inside, Outside, Depth
A proper caliper measures all three: outside diameter (OD), inside diameter (ID), and depth. On conduit work specifically, you'll use OD constantly. On box work, depth measurement for proper fitting installation. ID for verifying fitting thread specs. One tool, three measurements.
Accuracy in Field Conditions
A 6" digital caliper accurate to 0.01mm is more precision than you need in the field — but it means any real measurement error is yours, not the tool's. Clean the jaws before measuring. Zero it before you use it. Those two habits give you reliable readings every time.
What to Avoid
Extremely cheap calipers with plastic jaws. The jaw material matters for durability and accuracy under field conditions. Metal jaws, metal frame, decent IP rating for dust. The good ones aren't expensive — you don't need a Mitutoyo for electrical work. But the bottom-of-the-barrel options will fail on you.