TryBuildCalcLevel 1 EV Charger Circuit Calculator (120V Standard Outlet Charging)
Calculate your Level 1 charger circuit.
🕒 Last updated: August 29, 2026
Inputs
ℹ️Select your EVSE's charging level and amperage, or choose Custom to enter it directly.
ℹ️The EVSE's own nameplate rated continuous current — not the vehicle's onboard charger rating.
ℹ️Distance from the panel/breaker to the EVSE, one way — not round trip.
ℹ️The wire's own insulation rating (check the product's markings, e.g. THHN, THWN-2).
ℹ️Per NEC 110.14(C) — the breaker/panel/EVSE's own temperature rating. The calculator uses the lower of this and the insulation rating above.
Connection & Location
ℹ️Affects GFCI protection requirements per NEC 625.54.
Advanced (NEC Derating)
Cost
Recommended Circuit: 20A breaker, 12 AWG copper
For a 16.0A (1.9 kW) charger at 120V — sized by ampacity, not voltage drop
GFCI Protection
• Required — NEC 625.54 requires GFCI protection for all receptacles installed to connect EV charging equipment, regardless of location.
Ampacity Check
Design current: 20.0 A (125% continuous factor, NEC 625.41)
Minimum size by ampacity: 12 AWG
Derating factor applied: 1.00×
Final wire's derated ampacity: 25.0 A
Voltage Drop Check
Charger rated current: 16.0 A
Minimum size by voltage drop: 14 AWG
Allowed drop: 3.0%
Final wire's actual drop: 1.58% (1.90 V)
Circuit Summary
| System | 120 V, single-phase |
| One-way run length | 30.0 ft (9.1 m) |
| Connection / location | Plug-in, indoor |
| Small-conductor OCPD cap | 20 A (NEC 240.4(D)) |
Panel Impact (Informational)
| Service Size | % of Service Used by This Circuit |
|---|---|
| 100A | 20.0% |
| 125A | 16.0% |
| 150A | 13.3% |
| 200A | 10.0% |
| 225A | 8.9% |
This is a single circuit's share of a service, not a full load calculation — use the Panel Size Calculator to check your service has capacity for this plus everything else.
Assumptions Used
NEC 625.41 (125% continuous-load factor), NEC Table 310.16 ampacity, NEC 110.14(C) governing rating, NEC 240.4(D) small-conductor cap. Assumes a dedicated branch circuit (NEC 625.42) — not a shared/EMS-managed circuit. This is a reference estimate — confirm with a licensed electrician before installation.
Checking your panel has enough total capacity for this plus everything else? Panel Size Calculator →
Need to size the conduit for this and other conductors? Conduit Fill Calculator →
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete EV Charger Load Calculator.
Level 1 charger circuit sizing
Level 1 charging uses a standard 120V circuit — slower than Level 2, but sufficient for lower daily mileage or as a backup charging option.
This page is pre-set to a 16A charger on a plug-in (receptacle) connection, requiring GFCI protection per NEC 625.54.
- 16A × 1.25 = 20A design current, needing a standard 20A circuit — 12 AWG copper is the common pairing.
- A plug-in Level 1 EVSE connection always requires GFCI protection, regardless of location.
- Level 1 charging adds roughly 3-5 miles of range per hour — check whether it meets your actual daily driving needs.
EV Charger Circuit Formula: How Is It Calculated?
NEC 625.41's continuous-load treatment drives both the wire and breaker sizing.
Step 1 — Design Current
Design Current = Charger Rated Current × 1.25
Per NEC 625.41, EV charging equipment is always treated as a continuous load — this 125% factor applies regardless of how the charger is actually used.
Step 2 — Wire Size
Smallest AWG where: Derated Ampacity ≥ Design Current, AND
Voltage Drop at Charger Current ≤ Max Allowed %
The wire must satisfy both the design-current ampacity requirement and the voltage drop limit over the actual run length — whichever requires the larger wire governs.
Step 3 — Breaker Size
Recommended Breaker = smallest standard size ≥ Design Current
(capped by the wire's small-conductor OCPD limit, if lower)
Rounded up to a real NEC 240.6(A) standard breaker size, never a custom in-between value.
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Charger | 16.0A at 120V (1.9 kW) | Sets the base current before the continuous-load factor |
| Run Length | 30.0 ft | Sets the voltage drop check |
| Connection / Location | Plug-in, indoor | Sets the GFCI requirement |
Step 1 — Design Current
| Calculation | 16.0 × 1.25 |
| Design current | 20.0 A |
Steps 2-3 — Wire and Breaker Size
| Check | Result |
|---|---|
| Minimum size by ampacity (20.0A design current) | 12 AWG |
| Minimum size by voltage drop (3.0% max) | 14 AWG |
| Final wire (larger of the two) | 12 AWG |
| Breaker (design current rounded to standard size) | 20 A |
Therefore, for a 16.0A charger at 120V, you need 20A breaker, 12 AWG copper, with GFCI protection required.
Related Calculators
Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.