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
478 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 guidesSolar & Storage 6 min read
String Inverters vs Microinverters
A string inverter converts DC for a whole series of panels at one central unit: cheaper and simpler, but the shaded panel limits the string. Microinverters convert at each panel, isolating shade losses and giving per-panel monitoring, at higher cost and with more units on the roof.
Read the guideSolar & Storage 7 min read
What Is UL 3700? The Plug-In Solar Safety Standard
UL 3700 is the first US safety document written specifically for plug-in solar. It targets the hazards a normal inverter listing doesn't, such as an overloaded branch circuit, live plug blades, and GFCIs that can't see backfeed. As of October 2026, only components, not complete kits, had been confirmed certified to it.
Read the guideSolar & Storage 5 min read
Why Solar Shuts Off in a Blackout
Grid-tied solar shuts down in an outage by design, under IEEE 1547 anti-islanding requirements; otherwise the array would keep energising the utility line and endanger the crew repairing it. Adding a battery with proper islanding capability is what allows the system to keep running.
Read the guide04Gear
Gear picks built from spec sheets
16 buying guides comparing 83 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