Built for electricians, engineers, and serious DIYers.
VoltageDrop.calc is a free, browser-based voltage drop calculator that applies NEC Chapter 9 Table 8 and Table 9 resistance data to the industry-standard formulas for DC, single-phase AC, and three-phase AC circuits. Every calculation runs entirely in your browser — zero backend, zero data collection, zero logins.
What the Calculator Does
12V, 24V, 48V, and any custom DC voltage. NEC Table 8 copper and aluminum resistance at 75°C. Ideal for solar, RV, and battery systems.
120V and 240V single-phase circuits using NEC Table 9 AC impedance values. Adjustable conduit type and power factor.
480V and any three-phase voltage with correct √3 line geometry. Full effective impedance calculation per NEC Chapter 9 preamble.
Automatically recommends the minimum wire size that meets your target drop threshold — from 14 AWG to 1000 kcmil.
Full support for both conductor materials across all wire sizes. Switch instantly to compare resistance and voltage drop.
Enter distance in feet or meters. Resistance values shown in both Ω/kft and Ω/km for international cable sizing.
NEC Standards We Follow
Calculation accuracy depends on using the correct code-referenced resistance values. VoltageDrop.calc uses data sourced directly from the following NEC references:
Who Uses VoltageDrop.calc
Licensed Electricians
Quick field calculations for residential, commercial, and industrial circuits. Verify wire sizing before pulling cable on new construction, service upgrades, and panel replacements.
Electrical Engineers
Rapid feeder and branch circuit sanity checks during design. Validate voltage drop on 480V three-phase feeders, motor branch circuits, and power distribution studies.
Informed DIYers
Plan garage subpanels, EV charger circuits, solar system wiring, and home addition circuits. Understand the code requirements before speaking with your electrician.
Students & Apprentices
Learn the voltage drop formula, understand NEC Chapter 9 tables, and practice real-world wire sizing problems with instant visual feedback.
"Undersized wire is a fire hazard. Oversized wire is wasted money. The right wire size — calculated correctly — is what we're here for."
Our mission is to make authoritative, NEC-accurate voltage drop calculations accessible to everyone — from the master electrician on a job site to the homeowner planning a generator transfer switch.
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