The short answer
For one appliance and a number you can trust, a single local-display meter is the simplest tool: the Kill A Watt P4400 if you are happy to do the cost arithmetic yourself, or the P4460 if you want cost on the screen and a reading that survives being unplugged. Choose an energy-monitoring smart plug only if you want history in an app over days and weeks. Do not buy a four-pack to measure one thing, and do not put any of these on a space heater.
Decide in three questions
- Does the appliance plug into an ordinary wall outlet?
- Yes: continue.
- No (hardwired, or a large 240 V plug like a dryer or range): none of these devices can measure it. Use the nameplate and the calculator, or the appliance's EnergyGuide label.
- Is it within the meter's rated load, and not a heater?
- Fridges, freezers, dehumidifiers, TVs, computers, window fans, aquariums, chargers: usually fine. Check the rating on the meter's label against the appliance's label.
- Space heaters: no. CPSC guidance is to plug heaters directly into the wall; calculate them from the nameplate instead.
- Do you want a number now, or a history?
- A number for one appliance, read off a screen, no app or Wi-Fi: local-display meter.
- Day-by-day history you can look at from your phone, and you are comfortable with an app account and a 2.4 GHz Wi-Fi network: energy-monitoring smart plug.
The two types, compared
The table uses facts from each product's manual or manufacturer page. Where we could not confirm a value from a document, it says "not yet verified" rather than guessing. We have not tested any of these ourselves.
| Detail | Kill A Watt P4400 | Kill A Watt EZ P4460 | Kasa KP115 smart plug | Tapo P115 four-pack | Kasa KP125M four-pack |
|---|---|---|---|---|---|
| Pack | Single meter | Single meter | Single plug | Four plugs | Four plugs |
| Where you read it | On the meter | On the meter | In the Kasa app | In the Tapo app | In the Kasa app |
| What it records | kWh and elapsed time | kWh, elapsed time and cost | Energy use in the app | Energy use in the app | Energy use in the app |
| Keeps data if unplugged | No, resets | Yes | Not yet verified | Not yet verified | Not yet verified |
| Cost shown | No, use the calculator | Yes, at the rate you enter | No device display | No device display | No device display |
| Needs an app | No | No | Yes, plus 2.4 GHz Wi-Fi | Yes, plus 2.4 GHz Wi-Fi | Yes, plus 2.4 GHz Wi-Fi |
| Rated load | See unit label | 125 V, 15 A, 1,875 W | Not yet verified | Not yet verified | Not yet verified |
| Amazon | Check availability on Amazon | Check availability on Amazon | Check availability on Amazon | Check availability on Amazon | Check availability on Amazon |
The practical differences: the P4400 forgets its total the moment it loses power, so a tripped breaker or a curious family member ends your measurement. The P4460 keeps its total and can show cost at a rate you enter. Smart plugs show energy use in their app rather than on the device, so you can check from anywhere; how long readings are kept is not something we verified from a manual, and every reading depends on Wi-Fi, an account, and the app continuing to exist.
What none of them can measure
- Hardwired equipment: water heaters, furnaces, heat pumps, central AC, baseboards, well pumps. These are often the biggest loads in an older house, and a plug-in meter tells you nothing about them.
- 240 V appliances: electric dryers and ranges use a different outlet.
- Loads above the meter's rating. The P4460 manual specifies 125 V, 15 A, 1,875 W; the P4400's rating is printed on the unit. Exceeding a rating is a safety issue, not a measurement error.
- Space heaters, even small ones. Direct to the wall, per CPSC.
- Whole-house usage. That is what your utility meter is for; read it daily for a week before buying anything.
We have not measured these devices against a reference, so this guide gives no accuracy figures and makes no accuracy comparison between them. Manufacturer specifications are not a substitute for a test, and neither is this page.
Which one, for which job
P3 International Kill A Watt P4400
Single meterThe plain option. Plug it in, plug the appliance into it, come back in a few days and read the kWh. Then put that figure and the days into the calculator's meter mode. Its one real weakness is that any interruption to power resets the total, so pick an outlet nobody will disturb.
You want to measure one plug-in appliance at a time, read the number off the meter and do the cost arithmetic yourself.
Hardwired appliances, 240 V dryers or ranges, anything above the meter's rated load, wet locations, or a measurement you cannot afford to lose if the meter is unplugged.
- Confirm the maximum ratings printed on the unit label of the exact item you buy.
P3 International Kill A Watt EZ P4460
Single meterSame job, two conveniences: it keeps its totals through a power interruption, and it can display cost at the rate you enter. If you plan to move it from appliance to appliance over a winter, or the household has a habit of unplugging things, this is the one to get. The cost display only means something once you have typed in your own rate.
You want the same plug-in measurement but with cost shown on the device and readings that survive being unplugged or a power cut.
Hardwired appliances, 240 V dryers or ranges, loads above 15 A or 1,875 W, or wet locations.
TP-Link Kasa KP115
Single plugThe single-unit smart plug we could verify for the US. Choose it when you want to see a fridge's daily pattern from your phone, not just a total. It is a different model from the KP125M and we make no Matter claims for it. Read the current manual for the rated load before using it on anything substantial.
You want to watch one appliance's energy use over days from your phone and are comfortable with an app-connected plug.
Space heaters or other loads the plug is not rated for, critical appliances, or anyone who wants a reading without an account and Wi-Fi.
- Rated load limits should be read from the current manual before use with any high-draw appliance.
- Current seller and offer availability need checking at purchase time.
Multi-packs: only if you really have several appliances
Both Tapo P115 and Kasa KP125M are sold in the US as four-packs. Four plugs make sense if you genuinely want ongoing monitoring on four devices at once. They do not make sense for finding out what one freezer costs. No US single-pack of the Tapo P115 was verified; the only one-pack we found was a German-market variant, which is not a substitute.
TP-Link Tapo P115 (4-pack)
Four plugsA reasonable choice for four separate plug-in appliances with app history, if you are already comfortable with the Tapo app. Not a choice for one measurement.
You genuinely have four separate plug-in appliances to monitor and want app-based history for all of them.
Measuring a single appliance. Buying four plugs to measure one thing is the kind of purchase this site exists to talk you out of.
- No US single-pack verified; do not assume one exists.
- Rated load limits should be read from the current manual.
TP-Link Kasa KP125M (KP125MP4 4-pack)
Four plugsThe Matter-capable four-pack. TP-Link's support page lists a firmware release adding Matter energy reporting for the V1 hardware, so what you get depends on the hardware and firmware in the box; check before relying on it.
You have several appliances to monitor and want a Matter-capable plug; check the hardware and firmware version for the energy features you need.
Single-appliance measurement or heaters.
- Matter energy reporting depends on hardware version and firmware; verify on TP-Link's support page for your unit.
Check fit before you buy
- The appliance plugs into a standard outlet Hardwired and 240 V equipment cannot be measured with any of these.
- The appliance's label is within the meter's rated volts, amps and watts Check the meter's own label; the P4460 manual states 125 V, 15 A, 1,875 W. Ratings are safety limits.
- It is not a space heater CPSC: heaters go directly into a wall outlet, with nothing in between.
- The outlet is dry and indoors The P4460 manual restricts wet locations; smart plugs are indoor devices unless rated otherwise.
- You can leave it for several full days Short measurements miss compressor cycles and defrost heaters; the calculator warns below three days.
- For a smart plug: 2.4 GHz Wi-Fi and an app account are acceptable to you No Wi-Fi, no reading.
- Recall and model check on the day you buy A dated CPSC title search on 2026-09-07 returned nothing for these models; check again for the exact item.
Borrowing instead of buying
Many public libraries lend Kill A Watt meters, and some utilities and energy-efficiency programs do the same or run free audit schemes. If you have one appliance to check once, borrowing costs nothing and answers the question just as well. Buy a meter when you expect to measure several things over a season, or when you want to keep an eye on something that may be failing.
Once you have a reading, the calculator's meter mode turns kWh and days into a monthly cost, and the high-bill guide shows how to compare that with the change on your bill.
Sources and evidence
What we are relying on
- The P4400 accumulates kWh and elapsed powered time. Its accumulated readings reset when power is removed, and it has no on-device dollar calculation.
- Verified from the manufacturer or official document.
- A dated CPSC recall title search on 2026-09-07 returned no recall for the selected meters and plugs.
- Verified from the manufacturer or official document. Check the model and lot again immediately before buying.
- The P4460 lets you enter your electricity rate and shows cost projections on the device, and it retains accumulated measurements after a loss of power.
- Verified from the manufacturer or official document.
- The P4460 manual specifies measurement ranges up to 125 V rms, 15 A rms and 1,875 W and restricts use in wet locations. The unit label states the maximum ratings.
- Verified from the manufacturer or official document. A rating limit does not make every appliance suitable; follow both the meter and appliance instructions.
- The Kasa KP115 is sold in the US as a single energy-monitoring smart plug. It is a different model from the KP125M and does not inherit the KP125M's Matter claims.
- Verified from the current listing and manufacturer record; not a laboratory result. Current seller and offer availability still need checking before purchase.
- The documented US Tapo P115 package is a four-pack. No US single-unit P115 listing was verified.
- Verified from the current listing and manufacturer record; not a laboratory result.
- TP-Link's KP125M V1 support page lists a firmware release adding Matter energy reporting.
- Verified from the manufacturer or official document. Applies to the hardware version and firmware named on that page; not generalized to other versions, apps or the KP115.
What this page does not establish
- No hands-on testing or accuracy measurement has been performed on any device on this page.
- Prices, seller and stock are not shown or verified; confirm the current offer and pack on Amazon.
- Rated load figures for the smart plugs were not confirmed from a current manual and are marked as not yet verified.
Sources
- Kill A Watt P4400 operation manual, P3 International. Manufacturer document; read 2026-09-07.
- SaferProducts recall title search (Kill A Watt, P3 International, TP-Link, Kasa, Tapo), U.S. Consumer Product Safety Commission. Official guidance; read 2026-09-07. Dated title search only. No recall was returned for the selected meters or plugs. Not a guarantee.
- Kill A Watt EZ P4460 operation manual, P3 International. Manufacturer document; read 2026-09-07.
- Kasa Smart Plug Mini with Energy Monitoring, KP115 (1-pack), TP-Link. Manufacturer document; read 2026-09-07.
- Tapo P115 Mini Smart Wi-Fi Plug with Energy Monitoring (US), TP-Link. Manufacturer document; read 2026-09-07. US package documented as four units; no US single pack verified.
- KP125M V1 support and firmware downloads, TP-Link. Manufacturer document; read 2026-09-07. Firmware notes are dated; capabilities depend on hardware version and firmware.
- Keep warm and safe this winter: tips for using generators, furnaces and space heaters, U.S. Consumer Product Safety Commission. Official guidance; read 2026-09-07.
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