Why WattSimple
Numbers you can actually trust
Real specs, local electricity rates, and code-correct math, so the estimate matches your bill, not a generic default.
Per-model depth
Real specs for every EV, not one-size-fits-all defaults.
Per-state rates
Local electricity prices so estimates match your bill.
Electrical accuracy
Breaker and NEC math done right, where others are vague.
Instant & free
No sign-up, no email. Results update as you type.
01Calculators
Calculators that do the real math
37 free tools for EV charging, EV costs, home energy and solar: instant results, NEC-correct electrical sizing, and your own electricity rate.
Browse all calculators- Vehicle
- 2024 Tesla Model Y
- Battery
- 75 kWh
- Charge
- 20% → 80%
- Rate
- 16.5¢/kWh (US avg)
per session$8.24
50.0 kWh from the grid · 45 kWh into the battery · 10% charging loss
Try it with your carSpace Heater
1,500 W÷120 V=12.5 A
Amps = watts ÷ volts (single-phase, resistive load)
02Converters
Every electrical conversion, one tap away
34 converters for watts, amps, volts, kilowatt-hours, BTU and more; each one shows the formula behind the answer.
Open the converters03Guides
Plain-English guides, checked against the code
471 guides across 8 topics (EV charging, panels and wiring, backup power, solar and more) written to answer the question, not to pad the page.
Read the guidesWiring & Home Electrical Safety 7 min read
Open Ground Outlet: What the Tester Means and How to Fix It
An open ground reading means the receptacle's ground pin has no path back to the panel. Usually it's a three-prong receptacle on an old two-wire circuit, sometimes a broken or disconnected ground wire. The legal fixes are a real ground wire, a labeled GFCI, or a two-prong receptacle. A jumper to the neutral is not one of them.
Read the guideWiring & Home Electrical Safety 7 min read
Reverse Polarity Outlet: Why It's Dangerous and How to Fix It
A reverse polarity outlet has the hot wire on the neutral terminal and the neutral on the hot. Everything still works, but the parts a polarized plug is designed to keep dead, like a lamp's screw shell, stay energized with the switch off. The fix is moving two wires to the right screws, with the breaker off.
Read the guideWiring & Home Electrical Safety 6 min read
Two-Prong Outlets and Ungrounded Circuits
The NEC permits replacing an ungrounded two-prong receptacle with a GFCI labelled "No Equipment Ground": legal, and it provides real shock protection. It does not create a ground, so surge protectors and some electronics still will not have the path they need.
Read the guide04Gear
Gear picks built from spec sheets
15 buying guides comparing 80 products on manufacturer specs: chargers, outlets, testers, backup power and more. No invented prices, no fake ratings.
See the buying guidesEV charging
Backup power
| Breaker | Min. copper (NM-B) | Typical use |
|---|---|---|
| 15 A | 14 AWG | Lighting, general outlets |
| 20 A | 12 AWG | Kitchen, bath, garage outlets |
| 30 A | 10 AWG | Electric dryer, water heater |
| 40 A | 8 AWG | Electric range, 32A EV charger |
| 50 A | 6 AWG | Range, 40A EV charger, NEMA 14-50 |
| 60 A | 4 AWG | 48A EV charger, subpanel feed |
NEC 310.16 and 334.80 · confirm with your local code
05Reference
Reference charts you'll actually bookmark
13 look-up charts (wire and breaker sizes, appliance wattage and amperage, EV specs and connectors) each with its source.
All reference charts06State rates
Your state's rate changes the answer
Residential electricity rates for all 50 states and DC, plus average bills, EV charging costs and heat pump costs state by state.
Find your stateUS average 16.5¢/kWhEIA residential averages, ¢/kWh
- EV charger installers
- 611
- Solar installers
- 255
- States covered
- 51
07Installers
When it's time to call a pro
State-by-state directories of EV charger and solar installers, with ZIP search, for the jobs the calculator says need a licensed electrician.
Questions