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Best Energy Monitors and Plug-In Power Meters

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Every cost-to-run and amperage figure on this site starts from typical wattage and typical hours. Your appliance is not typical: an old fridge can use several times what a new one does, and a space heater's thermostat decides how many of its hours are really full power. Measuring replaces the estimate with your own number.

There are two tools, and the load decides which. A plug-in meter sits between the outlet and any corded 120 V appliance and records its real watts, amps and kilowatt-hours — no tools, nothing opened. It cannot measure anything hardwired or on a 240 V circuit (water heater, dryer, range, central AC, a Level 2 charger). A whole-home monitor can: its current sensors clip around the conductors inside the panel and log every monitored circuit at once, which is why installing one means working in a live panel.

Measure for a representative stretch — a full day for anything that cycles, like a fridge or freezer — then multiply the kilowatt-hours by your electricity rate. That is the number the calculators here estimate.

How we picked

  • Measures real kilowatt-hours over time, not just instantaneous watts
  • Rated for the load you want to measure (15 A plug-in, or the panel's service for a whole-home unit)
  • Safety listing from a recognized testing lab
  • No subscription needed to see your own data

We do not accept payment for placement and we do not publish star ratings we did not measure. Specifications come from each manufacturer's published spec sheet.

Side by side

ProductTypeBest forWarrantyRatingDisplayskWh counterAccuracySizeSensorsServiceDataConnectivitySolarListingSubscription
P3 International Kill A Watt P4400Plug-in power meterMeasuring what one plug-in appliance really uses6 months125 V AC max, 15 A max, 1,875 VA maxVolts, amps, watts, VA, Hz, power factor, kWh, elapsed time0.01–9,999 kWh (resets when unplugged)0.2% (manufacturer claim)5⅛ × 2⅜ × 1⅝ in, 5 oz———————
Emporia Vue 3 Home Energy Monitor (16 circuit sensors)Whole-home energy monitorMeasuring hardwired and 240 V loads, or every circuit at once1 year—————Two 200 A main sensors + sixteen 50 A circuit sensorsSplit-phase 120/240 V residential panels1-second readings, ±2% accuracy2.4 GHz Wi-Fi (Ethernet option); needs internetNet metering supported (not for solar tied in ahead of the panel)UL 61010, UL 2808None

The picks

#1 · Plug-in power meter

P3 International Kill A Watt P4400

Check price on Amazon — P3 International Kill A Watt P4400 (opens in a new tab)(paid link)

The plug-through meter that sits between an outlet and any corded 120 V appliance and shows its real volts, amps, watts and cumulative kilowatt-hours.

Best for: Measuring what one plug-in appliance really uses

Rating
125 V AC max, 15 A max, 1,875 VA max
Displays
Volts, amps, watts, VA, Hz, power factor, kWh, elapsed time
kWh counter
0.01–9,999 kWh (resets when unplugged)
Accuracy
0.2% (manufacturer claim)
Size
5⅛ × 2⅜ × 1⅝ in, 5 oz
Warranty
6 months
  • No tools, no panel, no app — plug it in, plug the appliance into it, read the screen
  • True-RMS volts and amps, so motor and electronic loads read correctly, not just heaters
  • Leave it for a day or a week and the kWh total is the number every cost estimate is guessing at
  • 120 V corded loads up to 15 A only — it cannot measure a 240 V dryer, range, water heater or anything hardwired
  • No cost display — multiply the kWh by your rate yourself (P3's P4460 EZ model does the math)
  • The counters reset if it is unplugged or the power blinks
Read the full write-up →

#2 · Whole-home energy monitor

Emporia Vue 3 Home Energy Monitor (16 circuit sensors)

Check price on Amazon — Emporia Vue 3 Home Energy Monitor (16 circuit sensors) (opens in a new tab)(paid link)

A panel-mounted monitor that clips current sensors around your mains and up to 16 branch circuits, logging each one's real power and kilowatt-hours to an app.

Best for: Measuring hardwired and 240 V loads, or every circuit at once

Sensors
Two 200 A main sensors + sixteen 50 A circuit sensors
Service
Split-phase 120/240 V residential panels
Data
1-second readings, ±2% accuracy
Connectivity
2.4 GHz Wi-Fi (Ethernet option); needs internet
Solar
Net metering supported (not for solar tied in ahead of the panel)
Listing
UL 61010, UL 2808
Subscription
None
Warranty
1 year
  • Measures what a plug-in meter can't — water heater, dryer, HVAC, EV charger, well pump
  • Every monitored circuit logged at once, so a stuck or cycling load shows up without guessing which to test
  • No subscription to see your own data
  • Installs inside the live panel — Emporia says installation should be done by a skilled person such as a licensed electrician
  • Sixteen circuit sensors cover most panels but not every breaker in a large one
  • Cloud-dependent: the app needs the monitor online
Read the full write-up →

Working out what you need before you buy? Read the heating, cooling & water heating guides.