How the calculator works
The estimate is plain arithmetic you can check yourself:
Vehicle energy = usable battery × (charge − driving reserve) × conversion efficiency
Total energy = vehicle energy + Powerwall energy
Runtime (hours) = total energy ÷ (daily load − daily solar) × 24Daily load comes from the appliances you pick (running watts × duty cycle × hours per day) or from the daily total on your utility bill. Peak load adds up every selected appliance running at once, plus the largest single motor start, and is compared with the vehicle's 11.52 kW Powershare output.
Tesla Model Y Powershare runtime
Every Model Y ordered in the U.S. or Puerto Rico on or after October 1, 2026 is Powershare-capable, and some earlier cars are too. Tesla's own backup estimates and our battery estimates by trim:
| Trim | Usable battery (estimate) | Tesla's backup estimate | This calculator* |
|---|---|---|---|
| Model Y Standard | 65–69.5 kWh | Up to two days | 1.8 days – 1.9 days |
| Model Y Premium RWD | 75–79 kWh | Over two days | 2.0 days – 2.1 days |
| Model Y Premium AWD | 75–82 kWh | Over two days | 2.0 days – 2.2 days |
| Model Y Performance | 75–82 kWh | Over two days | 2.0 days – 2.2 days |
*Added backup at Tesla's assumptions: 30 kWh/day, 90% charge, no driving reserve, 90% conversion efficiency. Tesla's estimates are official; battery capacities are third-party estimates. Open the calculator with Model Y.
Tesla Model 3 Powershare runtime
Every Model 3 ordered in the U.S. or Puerto Rico on or after October 1, 2026 is Powershare-capable, and some earlier cars are too. Tesla's own backup estimates and our battery estimates by trim:
| Trim | Usable battery (estimate) | Tesla's backup estimate | This calculator* |
|---|---|---|---|
| Model 3 Standard | 66–70 kWh | Up to two days | 1.8 days – 1.9 days |
| Model 3 Premium RWD | 75–82 kWh | Over two days | 2.0 days – 2.2 days |
| Model 3 Premium AWD | 75–82 kWh | Over two days | 2.0 days – 2.2 days |
| Model 3 Performance | 75–82 kWh | Over two days | 2.0 days – 2.2 days |
*Added backup at Tesla's assumptions: 30 kWh/day, 90% charge, no driving reserve, 90% conversion efficiency. Tesla's estimates are official; battery capacities are third-party estimates. Open the calculator with Model 3.
Assumptions
- Usable battery capacity is a third-party estimate because Tesla does not publish it. The calculator uses the low end of the range; the result shows the full range.
- Conversion efficiency defaults to 90% to cover inverter and standby losses. Tesla does not publish this. With these defaults the model agrees with Tesla's published backup estimates for every trim.
- Powerwall 3 and each Expansion unit add 13.5 kWh (official), starting full unless you change it.
- Appliance wattages are typical values. The nameplate on your appliance is the real number, and older units can draw much more.
- Solar is treated as a daily total subtracted from the load. The calculator does not model hour-by-hour solar, weather, battery heating in cold weather, or Powerwall reserve settings.
- With Powerwall, how vehicle and Powerwall output combine during peaks depends on how the system is configured. The peak check compares against the vehicle's 11.52 kW alone.
Sources
Every number on this page comes from one of these, labeled by type:
Max continuous real power 11.52 kW, LRA motor start 185 A, 240 V AC. Installation: Universal Wall Connector or Wall Connector 3 plus a Powerwall 3 system.
Powerwall 3 is compatible today. Tesla says Powerwall 2 and Powerwall+ support is coming via over-the-air update.
- OfficialTesla Support – Powershare (How much backup duration can my vehicle provide?)Checked 2026-10-20
Durations are Tesla estimates for an average U.S. home using 30 kWh per day with the vehicle at 90% state of charge.
Gen 3 Mobile Connector plus Tesla Outlet Adapter turns the charge port into a 120 V outlet (up to 20 A). Gen 2 Mobile Connector is not supported. maxOutputKw is derived (120 V x 20 A).
13.5 kWh energy capacity, 11.5 kW continuous, 185 LRA motor start.
Adds 13.5 kWh of energy capacity to a Powerwall 3 system. No inverter of its own.
Lists two packs: 72.0 kWh gross / 69.5 kWh net, and 64.0 kWh gross / 60.5 kWh net. The smaller pack cannot deliver the U.S. car's 321-mile EPA range, so the U.S. estimate uses the larger one.
Reports Edmunds' test: the 2026 Model Y Standard drove 337 miles (EPA 321) using 22.8 kWh per 100 miles.
- DerivedSite calculation from the Edmunds testChecked 2026-10-21
337 mi x 22.8 kWh/100 mi = 76.8 kWh from the wall. At 85–90% charging efficiency that is about 65–69 kWh usable.
Lists 79 kWh for MY2026 Model Y Premium RWD.
UK listing: 82 kWh battery capacity, 79 kWh usable.
- EstimateSite assumptionChecked 2026-10-21
The low end is held at 75 kWh so results don't overpromise: Tesla publishes no figure and earlier Long Range packs were around 75 kWh.
Lists 82 kWh for MY2026 Model Y Premium AWD.
Lists 82 kWh for MY2026 Model Y Performance.
EPA range 321 miles. Edmunds drove 339 miles using 23 kWh per 100 miles (EPA rating 24 kWh/100 mi).
- DerivedSite calculation from the Edmunds testChecked 2026-10-21
339 mi x 23 kWh/100 mi = 78 kWh from the wall. At 85–90% charging efficiency that is about 66–70 kWh usable. EVKX lists 51 kWh for a MY2026 'Model 3 Standard' with no range figure; that cannot deliver the U.S. car's 321-mile EPA range, so it is not used.
Lists 82 kWh for MY2026 Model 3 Long Range RWD (European naming for the long-range pack).
Lists 82 kWh for MY2026 Model 3 Long Range AWD (European naming for the long-range pack).
Lists 82 kWh for MY2026 Model 3 Performance.
Typical running and starting watts for common U.S. appliances. Real values vary widely by model and age; the nameplate on the appliance is the authoritative number. The DOE page explains how to estimate usage from the nameplate.
- EstimateSite assumptionChecked 2026-10-20
Combined allowance for inverter conversion and standby losses. Tesla does not publish this figure. With the battery estimates in this repository, 90% reproduces Tesla's published duration claims (see tests/calibration.test.ts).
- EstimateSite assumptionChecked 2026-10-20
Rough real-world average used only to translate the reserved battery into miles. Actual efficiency varies with speed, temperature and trim.
Frequently asked questions
How long can a Tesla Model Y power my house with Powershare?
Tesla estimates that Model Y Premium and Performance can extend home backup by over two days, and Model Y Standard by up to two days. Those figures assume a home using 30 kWh per day and a car at 90% charge. Running only essentials such as the fridge, lights and Wi-Fi can stretch that to a week or more; central air conditioning shortens it. Use the calculator with your own loads for a personal estimate.
How long can a Tesla Model 3 power my house?
Tesla gives the same estimates as Model Y: over two days for Model 3 Premium and Performance, and up to two days for Model 3 Standard, at 30 kWh per day and 90% charge. The calculator above lets you change the charge level, driving reserve and appliances.
Does Powershare work without a Powerwall?
For Model 3 and Model Y, Powershare Home Backup currently requires Powerwall 3 plus a Wall Connector 3 or Universal Wall Connector. Tesla says Powerwall 2 and Powerwall+ support is coming. Without Powerwall, a Gen 3 Mobile Connector with the Tesla Outlet Adapter turns the charge port into one 120 V outlet (up to 20 A) for plug-in devices. Cybertruck can back up a home without Powerwall using a Powershare Gateway.
Can Powershare run my central air conditioner?
Often, yes, but it depends on the unit and everything else running. The vehicle supplies up to 11.52 kW continuous, and Tesla lists 185 A locked-rotor (LRA) motor-start capability with Powerwall. A typical 3-ton AC uses about 3.5 kW while running but draws a short surge when the compressor starts. Compare the LRA on your outdoor unit's nameplate, and expect AC to be the largest drain on runtime.
How much battery should I keep for driving?
Powershare stops discharging at the limit you set, so keep enough to reach a charger or leave if the outage drags on. Local chargers may be down too. The calculator defaults to 20%, which is roughly 50 to 60 miles of range on Premium trims.
Why is the battery capacity an estimate?
Tesla does not publish usable battery capacity for Model 3 or Model Y. We use third-party estimates, show the range, and default to the low end so results don't overpromise. If you know your car's usable capacity, enter it under Advanced assumptions.
Does solar extend Powershare backup?
Yes. Tesla says solar is compatible with Powershare and extends backup duration. Grid-tied solar only keeps working in an outage when a battery system such as Powerwall is running the home, so the calculator ignores solar when no Powerwall is selected.
Related tools
Changelog
- 2026-10-21: Re-checked every third-party battery source. Model Y Standard and Model 3 Standard estimates now use U.S. EPA ratings and Edmunds range tests (65–69.5 and 66–70 kWh).
- 2026-10-20: First release: Powershare runtime estimates for Model Y and Model 3, and the compatibility checker.
Disclaimer
This calculator is a planning estimate, not an electrical engineering assessment. Actual backup time depends on your equipment, configuration, weather and usage. Have a licensed electrician or Tesla Certified Installer design and verify any backup system. Not affiliated with Tesla, Inc.