Watts to Amps Calculator: Watt-Hours, Battery Size and Runtime

Watts to amps: for DC, divide watts by volts; for single-phase AC, divide watts by (volts × power factor). For example, 1,200W at 120V is 10A when power factor is 1. For portable backup supplying a steady 100W for eight hours, our pick among these sizes is the Anker SOLIX C2000 Gen 2: the 1,024Wh alternative falls short under the assumptions below.

Quick picks

• Small-load pick — EcoFlow RIVER 3 Plus: 286Wh and 600W continuous AC output.
• Middle-size pick — EcoFlow DELTA 3 Plus: 1,024Wh and 1,800W continuous AC output.
• Longer-runtime pick — Anker SOLIX C2000 Gen 2: 2,048Wh and 2,400W continuous AC output.

Start with the smallest size that clears your energy, output and startup checks. The picks cover US standalone stations; match the output voltage and regional version to your appliances.

1. 1

   Convert current

   Use the load's voltage and, for AC, its power factor.

2. 2

   Budget energy

   Multiply real watts by hours, then account for losses and station overhead.

3. 3

   Check appliance fit

   Verify continuous output and starting demand separately.

Watts to amps calculator: choose AC or DC first

Use this calculator worksheet with your own inputs. Record the voltage at the load and its electrical input watts before calculating current.

The DC relationship comes from Victron's electrical theory. For AC, P3's meter manual defines PF = W ÷ (RMS volts × RMS amps); rearranging gives the current equation above. Victron distinguishes watts from VA: watts are real power; VA is apparent power.

Worked conversions for a 1,200W single-phase AC load:

The power factors here are example inputs. Lower power factor raises current for the same watts and voltage; it is separate from inverter efficiency.

Use the device's electrical input watts. If power factor is unknown, use measured current or ask the appliance maker; assuming PF 1 can understate current. These AC equations cover single-phase loads, not three-phase systems.

Input checks: use positive voltage, nonnegative watts and time, and an AC power factor above 0 and no higher than 1. Keep unknown voltage or power factor marked as unknown; substituting zero makes the division invalid. Measured elapsed time must also be positive when calculating average power.

For battery-side current behind an inverter, use battery voltage and allow for inverter losses. Outlet current and battery current need different voltages.

What is a watt-hour? Calculate energy before capacity

Energy (Wh) = real power (W) × time (hours). A watt is power at a moment; a watt-hour is energy used over time. EIA's example is a 40W bulb for five hours: 40 × 5 = 200Wh. A kilowatt-hour equals 1,000Wh.

Enter time in hours; divide minutes by 60 first. For several devices, calculate each device's watt-hours and add them. Separately add the watts of devices that will run together for the continuous-output check. A short high-power task can need little energy yet exceed an inverter's output limit.

Watt-hours to amp-hours: use battery voltage

Ah = Wh ÷ nominal battery V. Conversely, Wh = Ah × nominal battery V. Victron's battery-sizing guide explains this conversion. Do not divide by the AC outlet voltage when asking for the battery's amp-hour capacity.

For an illustrative 1,200Wh, the nominal energy equivalents are:

These describe the same nominal energy at different voltages, before losses. For a real model check, Anker lists its C2000 Gen 2 battery as 51.2V / 40000mAh / 2,048Wh: that is 40Ah, and 51.2 × 40 = 2,048Wh. Compare sealed stations in Wh rather than comparing Ah without voltage.

Power station runtime calculator: show the assumptions

The loss-free ceiling is hours = battery Wh ÷ load W. A more useful approximation includes usable discharge, inverter efficiency and overhead. BLUETTI's Elite 100 V2 manual publishes this form:

Estimated hours = capacity Wh × usable fraction × inverter efficiency ÷ (load W + overhead W).

For the comparisons here, assume a full starting charge, 90% usable capacity, 90% efficiency and 10W overhead, with no recharging. BLUETTI specifies 90% depth of discharge, efficiency over 90% and about 10W self-consumption for its own model; we round efficiency down for this illustrative scenario. These are not measured loss figures for the picks.

The overhead here follows BLUETTI's published denominator convention. When idle consumption is specified at the battery, the energy balance instead gives hours = usable battery Wh ÷ [(AC load W ÷ efficiency) + battery-side idle W]. For USB or DC output, use that output's conversion losses.

Worked estimates and comparison

The capacities and output limits below are from EcoFlow RIVER, EcoFlow DELTA and Anker. Runtime columns are our rounded arithmetic using the shared assumptions above, not manufacturer runtime claims.

For the 100W column, the substitutions are:

• Small: hours ≈ 286 × 90% × 90% ÷ (100 + 10) ≈ 2.
• Medium: hours ≈ 1,024 × 90% × 90% ÷ (100 + 10) ≈ 7.5.
• Larger: hours ≈ 2,048 × 90% × 90% ÷ (100 + 10) ≈ 15.

Notice how a high output rating does not imply long runtime at that output.

• EcoFlow RIVER 3 Plus286Wh
• EcoFlow DELTA 3 Plus1024Wh
• Anker SOLIX C2000 Gen 22048Wh

Source: Maker specifications linked above; these are capacities, not usable AC energy.

What size power station do I need?

Rearrange the same approximation: required capacity Wh ≈ target hours × (load W + overhead W) ÷ (usable fraction × efficiency).

For a hypothetical 100W load for eight hours, using our shared assumptions: required Wh ≈ 8 × (100 + 10) ÷ (90% × 90%) ≈ 1,100. The 1,024Wh pick falls short of that target in this scenario; consider the 2,048Wh class if the output and startup checks also pass. Add your own reserve for uncertainty rather than planning to reach shutdown exactly.

Check running power and motor-start surge separately

Add simultaneous running loads and keep the total within the station's continuous rating and each port's limits. Then obtain the appliance's starting requirement and check the station's supported surge and duration with the maker. BLUETTI warns that some motors and compressors start at two to four times rated power; that is a warning, not a universal sizing multiplier.

• Yes: Output voltage, running watts and port ratings match the load
• Yes: Startup demand is confirmed for the actual appliance
• Partly: A peak-watt figure still needs appliance-specific confirmation
• No: Extra watt-hours alone do not raise the inverter's rated output

For cycling loads, use energy over a representative period to estimate average watts; keep running and startup demand for the output checks. A compatible plug-in meter can record energy and elapsed time: average W = recorded kWh × 1,000 ÷ hours. Follow the meter's ratings; P3's manual explains those readings. Our refrigerator wattage guide covers appliance-specific sizing instead of assuming every fridge draws the same power.

Small-load pick: EcoFlow RIVER 3 Plus

Choose it when the small-station estimate covers your session: EcoFlow specifies 286Wh, 600W continuous and 1,200W surge. Its 100W USB-C output is an alternative to AC for compatible devices; confirm their input requirements.

Variant check: keep Plus in the model name. This is the standalone station. EcoFlow offers an EB300 (286Wh) or EB600 (572Wh) extra battery, reaching 858Wh with the larger battery. Check package contents: an extra battery adds stored energy; a solar panel supplies recharging.

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Middle-size pick: EcoFlow DELTA 3 Plus

Choose it when the medium estimate fits: 1,024Wh, 1,800W continuous and 3,600W surge, with extra-battery support. On November 2, 2026, EcoFlow's page showed both Out of Stock and late-November preorder shipping for the base option. Confirm availability and delivery before relying on it for an imminent outage.

Variant check: choose the Plus model and the intended package. The official extra-battery kit lists 2,048Wh while retaining 1,800W output. Solar-panel kits add charging equipment. EcoFlow's X-Boost figures conflict: the spec table says 2,200W, while feature copy says over 2,600W. Use the unambiguous 1,800W continuous rating for sizing here.

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Longer-runtime pick: Anker SOLIX C2000 Gen 2

Choose it when the larger energy estimate is needed: Anker specifies 2,048Wh, 2,400W continuous and 4,000W peak. Its published 9W idle consumption also shows why station overhead deserves its own input; we retain the shared scenario above for comparison.

Variant check: retain Gen 2 in the model name. The compatible expansion is BP2000 (Gen 2); Anker describes total capacity up to 4kWh. Its panel bundle, expansion-battery bundle and multiple-station packs are different selections. Select a battery for stored energy, a panel for recharging, or separate stations for separate locations.

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How we choose

We compare manufacturer specification tables and model-specific manuals, using electrical relationships from official technical documentation. The recommendations follow capacity, continuous output and expansion needs; the runtime figures are calculations, not physical tests. We reuse the site's verified records for these exact standalone models.

The estimate stops at its assumptions: use your starting charge and reserve setting, actual load pattern and model-specific losses. Check automatic output shutdown settings for small loads: BLUETTI's manual, for example, warns that ECO mode can stop output after low-load operation. Do not count future solar charging in an outage plan without a separate charging estimate.

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Verdict

Calculate current with the correct voltage and AC power factor, energy with watts × hours, and runtime with losses and overhead visible. Choose RIVER 3 Plus for a small energy budget, DELTA 3 Plus for the middle class when delivery fits, or C2000 Gen 2 for a larger budget after checking output and startup demand. Continue to our portable power station guide for broader picks or our home battery backup guide for installed systems; house-connected backup requires a licensed electrician and permits where required.