Voltage drop calculator
Teaching estimate only. Uses simplified copper resistance per thousand feet (one-way conductor) and assumes roughly balanced two-wire current path. Real installs need temperature correction, conduit fill, harmonics, power factor, terminations and the current NEC edition — plus a licensed professional.
Approx voltage drop (round trip I×R)5.79 V
As % of nominal system V2.41%
Key takeaways
- Common AWG sizes from 14 through 4/0 in one dropdown.
- Shows both volts dropped and percent of nominal.
- Big red banner repeats non-design intent.
- Pairs with Housecall or Jobber line items after you confirm amp draw.
- No upload of site photos or plans.
Who built this
ContractorHQ is edited by Bernard Guido — 25+ years in trade operations and software. These utilities follow the same quality bar as our reviews: fast pages, honest disclosure, and tools that stay useful without selling your data.
Frequently asked questions
Is this code compliant?
No. It is a ballpark for conversations in the van. Final conductor sizing belongs to a licensed designer using the adopted NEC and local amendments.
Why round-trip I×R?
Current goes out and back; we double the one-way resistance for a simple two-wire approximation.
Aluminum conductors?
Not in this table. Aluminum needs different constants and terminations — use your office worksheet.
AC vs DC?
We use DC-style resistance as a first-order guess for short runs. Long feeders with high X/R need power-factor aware calcs.