WattRunTime.com
Language

Device measurement guide

How to Measure Device Watts for Runtime Planning

A meter reading is useful only when you know the device mode, output path, and measurement interval behind it.

Core concept

Read watts after a steady load settles; record energy over time for a cycling load.

Planning impact

Average watts calculated from Wh divided by hours already include off-cycle time, so do not apply duty cycle again.

What to verify

Follow the meter and device instructions, stay within ratings, and never open electrical equipment.

Average power (W) = energy used during the test (Wh) / elapsed time (hours).

How to Measure Device Watts for Runtime Planning

A meter reading is useful only when you know the device mode, output path, and measurement interval behind it.

Steady and cycling loads need different methods

A stable lamp, router, or charger can be read in watts after it settles. A refrigerator, dehumidifier, or thermostatic load should be observed through multiple cycles: record Wh and elapsed time, then divide Wh by hours.

Record the operating state

Write down the device model, mode, settings, ambient conditions, output path, meter model, and test time. A number without those conditions is not reusable evidence for another setup.

Keep startup demand separate

A normal plug-in energy meter may not capture a brief startup peak. Use an attributed manufacturer starting value or equipment intended for inrush measurement; leave the value unknown when neither is available.

Measure before you estimate

Use this workflow for an intact plug-in device that is within the meter rating. Record unknowns instead of filling them with guesses.

Safety boundary

Follow the meter and device manuals. Use a correctly rated, intact plug-in meter and outlet. Do not open equipment, remove covers, probe conductors, or measure hardwired or high-voltage equipment yourself. For critical medical backup, follow the device manufacturer's power guidance.

Measurement workflow

  1. Identify the exact device, normal operating mode, settings, and power path you plan to use.
  2. For a steady load, let it settle and record watts. For a cycling load, record Wh and elapsed time across multiple complete cycles.
  3. Calculate average watts as Wh divided by hours. Do not apply duty cycle again to that full-cycle average.
  4. Record startup demand separately only when the manufacturer or suitable measurement equipment provides it.
  5. Keep the date, meter, conditions, source, and unknown fields with the value before using it in the calculator.

WattRunTime.com

Device-load measurement worksheet

Device brand and model
 
Operating mode and settings
 
Measurement date and ambient conditions
 
Output path, voltage, and adapter
 
Meter model and rating
 
Start time, end time, and total interval
 
Steady power reading (W)
 
Energy over the interval (Wh)
 
Calculated average power (W)
 
Startup value, source, and remaining unknowns
 

Average W = measured Wh / elapsed hours

Open runtime calculator

Evidence and review

These sources support the definitions and planning method. Calculator results are still estimates, not measurements or guarantees.

Engineering review
Primary sources
2

Use the measured average

Enter a steady watt reading or a full-cycle average in the runtime calculator. Use 100% duty cycle for an average that already includes on and off periods.

Loading calculatorPreparing calculator
Power station model
EcoFlow DELTA 2
Power station modelEcoFlow DELTA 2
Battery capacity (Wh): 1024 WhContinuous output rating (W): 1800 WSurge output rating (W): 2700 W
Estimated runtime13h 3m8h 10m – 16h 13mEstimated runtime: 13h 3m, 8h 10m – 16h 13m
Output path

Estimated runtime

13h 3mEstimated runtime: 13h 3m

This setup has comfortable headroom for overnight use, assuming the wattage estimate is realistic.

Usable energy783 Wh
Average load60 W
Fixed station overheadUnknown (not included)
Running watts60 W
Max surgen/a
Conservative8h 10m
Estimated13h 3m
Optimistic16h 13m

Conservative assumes harder conditions; optimistic assumes favorable conditions.

Show your work

Rated Wh is reduced by efficiency, reserve, battery health, and temperature before it is divided by average load.

Rated battery1024 WhBattery capacity (Wh): 1024 Wh
Usable energy783 Wh1024 Wh x 85% x 90% x 100% x 100%
Average load60 W60 W running, 60 W average after duty cycle and quantity
Fixed station overheadUnknown (not included)60 W / 85% = 70.6 W battery draw; fixed overhead is unknown and excluded
Estimated runtime13h 3m783 Wh / 60 W = 13h 3m
  • 1024 Wh nominal battery capacity
  • AC inverter output path
  • 85% conversion efficiency
  • 10% reserve kept unused
  • 60 W average load from 1 load
  • 100% battery health
  • 0% temperature loss
  • Fixed station overhead unknown; not included
  • This is an estimate. Real runtime changes with load, temperature, battery age, AC/DC output, and device behavior.

This link contains the numeric values you entered, but not custom load names.

Source-Backed Next Steps

WattRunTime.com

WattRunTime estimate

Estimated runtime

13h 3mThis setup has comfortable headroom for overnight use, assuming the wattage estimate is realistic.
Usable energy783 Wh
Average load60 W
Fixed station overheadUnknown (not included)
Running watts60 W
Max surgen/a

Runtime range

Conservative8h 10m
Estimated13h 3m
Optimistic16h 13m

Show your work

Rated Wh is reduced by efficiency, reserve, battery health, and temperature before it is divided by average load.

Rated battery1024 WhBattery capacity (Wh): 1024 Wh
Usable energy783 Wh1024 Wh x 85% x 90% x 100% x 100%
Average load60 W60 W running, 60 W average after duty cycle and quantity
Fixed station overheadUnknown (not included)60 W / 85% = 70.6 W battery draw; fixed overhead is unknown and excluded
Estimated runtime13h 3m783 Wh / 60 W = 13h 3m

Assumptions

  • 1024 Wh nominal battery capacity
  • AC inverter output path
  • 85% conversion efficiency
  • 10% reserve kept unused
  • 60 W average load from 1 load
  • 100% battery health
  • 0% temperature loss
  • Fixed station overhead unknown; not included

Warnings

  • This is an estimate. Real runtime changes with load, temperature, battery age, AC/DC output, and device behavior.

Continue with your recorded load

Check duty cycle, output path, and startup demand before relying on the result.

Load behavior guide

Duty Cycle Explained

Some devices do not draw their running watts all the time. Duty cycle is how the calculator turns cycling behavior into average load.

Output power limits

Surge Power vs Continuous Power

Continuous power is the load an inverter can support on an ongoing basis. Surge, peak, or starting power is a higher short-duration limit. A device must fit both limits, but a peak number is never a substitute for continuous output.

Efficiency guide

Inverter Efficiency Losses

AC is convenient, but the inverter changes battery energy into wall-style power and some energy is lost as heat.

Measurement FAQ

Measure steady and cycling device loads safely, record the conditions, and enter a defensible average wattage in a battery runtime calculator.

Should I enter average watts and a duty cycle?

Not when the average came from Wh divided by a representative interval. That average already includes the off periods, so use 100% duty cycle. Use a separate duty-cycle value only with on-cycle running watts.

How long should I measure a cycling device?

Long enough to include multiple representative on and off cycles. Longer tests usually capture thermostat, door-opening, and ambient effects better; record the actual interval instead of claiming a universal duration.