Turn a borrowed meter reading into a real electricity cost
Record the accumulated kWh and elapsed time from a Kill A Watt or compatible plug-in meter. This page converts that test into daily, monthly, and yearly energy cost—without ads, affiliate links, accounts, or email collection.
- Works with any kWh reading
- Editable local rate
- CC BY 4.0
Plug-in meter cost calculator
Enter the totals shown after a representative test. Results update as you type.
- Average power
- 50 W
- During this test
- $0.20
- Per day
- $0.20
- Per 30 days
- $6.12
Based on 1.2 kWh measured over 24 hours.
How to run a useful meter test
- 01
Check compatibility
Confirm voltage, current, wattage, grounding, and load type for both the meter and appliance. Never use a damaged meter.
- 02
Clear old readings
Reset accumulated kWh and elapsed time using the instructions for the exact model in the library kit.
- 03
Measure a normal cycle
A lamp may need only a short stable test. A refrigerator, dehumidifier, or fan that cycles needs a longer representative period.
- 04
Write down kWh and hours
Record both values before unplugging. An instant watt reading alone cannot describe a changing load over time.
- 05
Use your local rate
Enter the per-kWh energy charge from your bill. The calculator does not allocate fixed service charges to one appliance.
P4400 vs P4460 EZ
Both can supply the kWh and elapsed-time values this calculator needs.
| Feature | P4400 | P4460 EZ |
|---|---|---|
| Accumulated kWh | Yes | Yes |
| Elapsed test time | Yes | Yes |
| Enter electricity rate | Calculate separately | On-device entry |
| Cost forecasts | Use this calculator | Week, month, and year |
| Published maximum | 115 V, 15 A, 1,875 VA | 115 V, 15 A, 1,875 VA |
Plug-in electricity meter measurement log
Use one row per appliance. Record kWh and elapsed time before resetting the meter.
| Appliance | Meter model | Test hours | Measured kWh | Projected yearly cost | Notes |
|---|---|---|---|---|---|
Which appliance used the most energy per day?
Was the test long enough to capture a normal operating cycle?
What change, if any, would reduce avoidable use without affecting safety?
Reusable under CC BY 4.0. Credit: HowMuchWatts.com/kill-a-watt-meter-guide/
A plug shape is not a compatibility check
Follow the meter and appliance manufacturers’ instructions. Motors, compressors, pumps, and heaters can have startup or continuous-load requirements that make a nominal wattage insufficient. Do not use a plug-in meter on hard-wired equipment or outside its listed voltage, current, power, grounding, and load conditions.
A meter measures use; it does not save electricity by itself. If a product instead claims to reduce a typical residential bill merely by plugging in, review the evidence and safety certification carefully.
Sources and reuse
- P3 International P4400 operation manual — readings, accumulated kWh, elapsed time, and ratings.
- P3 International P4460 product page — cost forecasts, accuracy claim, battery backup, and ratings.
- Vancouver Public Library power-meter instructions — a current public-library lending workflow.
- NIST residential power-factor guidance — why passive correction boxes do not reduce a typical household bill.
Specifications and source links checked August 12, 2026. This guide uses published information and is not a hands-on laboratory review.