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Nominal mains voltage (North America)

V120=120 VV_{120} = 120\ \text{V}
Value120 V
Use in the calculator →
StatusTypical value: varies by about ± 6 V in practice
SourceANSI C84.1: nominal system voltage, Range A tolerance
CategoriesElectromagneticEngineering & Trade
Nominal mains voltage (North America) in every voltage unit
UnitValue
volt120 V
millivolt120,000 mV
kilovolt0.12 kV
picovolt120,000,000,000,000 pV
nanovolt120,000,000,000 nV
microvolt120,000,000 μV
megavolt0.00012 MV
gigavolt1.2000000e-07 GV

Learning zone

Edison's original DC distribution ran at 110 V because that was what his carbon-filament lamps liked, and the number survived the switch to alternating current by inertia. It drifted upward over the decades (110, then 115, then 117) as utilities raised voltage to squeeze more power through existing copper, and settled at a nominal 120 V. Residential service arrives as 240 V centre-tapped, giving two 120 V legs for lighting and receptacles and the full 240 V for ranges, dryers and air conditioning.

ANSI C84.1 defines the tolerance rather than a single number: Range A is 114 to 126 V at the utilisation point, so any calculation that treats 120 V as exact is already working to about ±5%. That band is why the National Electrical Code caps branch-circuit voltage drop at 3% and total feeder-plus-branch drop at 5%, and why motors carry a nameplate utilisation voltage of 115 V rather than 120.

Used by 3 solvers

Percent Voltage Drop

%Vd=100 VdVs\%V_{d} = \frac{100 \, V_{d}}{V_{s}}

RMS and Peak Voltage

Vrms=Vpeak2V_{rms} = \frac{V_{peak}}{\sqrt{2}}

Voltage Drop, Single Phase

Vd=2ρLIAV_{d} = \frac{2 \rho L I}{A}
Revised 16 October 2026
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formula.expert. (2026, October 16). Nominal mains voltage (North America). https://formula.expert/constants/mains-voltage-north-america