What size power station do I need?
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Add the things you want to power, how many watts each uses, and how many hours a day you'll run them. The calculator tells you two things to look for on a spec sheet:
- Capacity (Wh): how much energy the battery stores. This decides how long things run.
- Continuous AC output (W): how much it can power at once from its mains sockets, plus the surge rating for appliances with a start-up spike.
It shows every step of the working, using the assumptions on our methodology page. Estimates only: we haven't tested any power station.
Fill in what you know. Results update as you type. Leave advanced settings alone unless you know better figures.
Advanced settings (efficiency, depth of discharge, derate)
Solar top-up (optional)
What to look for
Estimate only. Real runtime varies. Battery age and temperature, how hard the inverter is working, appliances that cycle on and off, start-up surges and the power station's own standby use all change the result. Always check your appliance's rating plate and your power station's manual, and don't rely on this for medical equipment.
Example starting points
The calculator's "start from an example" list fills in these. The appliance watts are from the published sources below; the hours and days are illustrative, so edit them.
| Example | What's in it | Rated capacity | AC continuous | AC surge |
|---|---|---|---|---|
| Tent weekend | Two days off-grid: a 12 V cool box, phones and a lamp. | 766 Wh (500–1,000 Wh) | 8 W | 8 W |
| Van weekend | Two days in a campervan: cool box, diesel heater, laptop, Starlink, lights and phones, with a 200 W panel in October. | 2,092 Wh (2,000 Wh and over) | 181 W | 181 W |
| 12-hour winter power cut | One evening and night at home: fridge-freezer, router, lights, phones and an electric blanket. | 3,051 Wh (2,000 Wh and over) | 634 W | 1,834 W |
How the sizing works
The calculator works backwards from your appliances. Every step is shown with your numbers:
(AC appliances ÷ inverter efficiency, DC/USB ÷ DC conversion efficiency)
energy needed = one day's energy × days without recharging
with solar: larger of one day's energy and (one day's energy − solar Wh a day) × days
usable capacity = energy needed × (1 + safety margin)
rated capacity = usable capacity ÷ (depth of discharge × (1 − derate))
AC continuous output: at least the AC watts running at once; ideally that ÷ 0.8
AC surge output: at least AC running watts + the largest single (start-up W − running W)
solar to replace a day in a day = one day's energy ÷ (peak sun hours × solar factor)
With solar we never size below one full day's use, because the battery still has to cover nights and dull days. The "recommended" continuous figure keeps the inverter at or below 80% of its rating, the same threshold the runtime calculator warns at.
Where to find your appliance's watts
- The rating label or the manual. This is the most accurate figure for your appliance.
- Our presets use typical figures from the Centre for Sustainable Energy's Energy Savers list, or the maker's spec sheet, which the tool cites.
- Things with a thermostat (fridges, heaters, blankets) don't run flat out all the time. Enter the hours they actually draw power if you know them, or use the full hours for a cautious answer.
Reading the result against a spec sheet
- Compare your rated capacity figure with the Wh on the maker's spec page.
- Check the continuous AC output is above your AC watts, and the surge rating covers the start-up peak.
- High-power heating appliances (kettles, heaters, hair dryers) may need more than the continuous rating. Some makers offer a boost mode for heating devices above the rated output (EcoFlow X-Boost, Anker SurgePad, BLUETTI Power Lifting). Check the maker's description of what it supports. See kettle.
- Then see the stated specs side by side in our power station spec table.
What the size bands mean
We group the rated capacity into four classes so you can compare spec sheets. These are capacity classes only, not product recommendations: the right model also depends on its outputs, ports, weight and charging.
- Under 500 Wh: The smallest class of portable power station.
- 500–1,000 Wh: A mid-size class.
- 1,000–2,000 Wh: A large class.
- 2,000 Wh and over: The largest class; some models in this range take extra battery packs.
Worked example: van weekend
Two days in a campervan: cool box, diesel heater, laptop, Starlink, lights and phones, with a 200 W panel in October. The hours are example usage, not measurements; change them to match yours.
| Appliance | Type | Running | Start-up | Hours/day |
|---|---|---|---|---|
| 12 V compressor cool box | DC | 9.12 W | – | 24 h |
| Diesel heater (12 V) | DC | 29 W | – | 8 h |
| Laptop (mains charger) | AC | 65 W | – | 2 h |
| Starlink (Standard kit) | AC | 100 W | – | 3 h |
| LED bulb or lamp | AC | 8 W × 2 | – | 4 h |
| Phone charging (USB) | DC | 5 W × 2 | – | 2 h |
Days without recharging: 2. Solar: 200 W panel lying flat on the roof, London in October (1.86 peak sun hours, PVGIS 2014–2023 average). Defaults: LiFePO4 (90% depth of discharge), 90% inverter efficiency, 95% DC efficiency, 20% safety margin.
- Energy for one day, from the battery:
Σ (W × quantity × hours ÷ efficiency)
9.12×24÷0.95 + 29×8÷0.95 + 65×2÷0.9 + 100×3÷0.9 + 8×2×4÷0.9 + 5×2×2÷0.95 = 1,044.55 Wh - Solar top-up:
min(panel W, max input W) × solar factor × peak sun hours = Wh/day; shortfall = daily use − solar
200 W × 0.7 × 1.86 h = 260.4 Wh/day; 1,044.55 − 260.4 = 784.15 Wh/day shortfall - Energy the battery must hold:
larger of one day's use (or the whole period if under a day) and shortfall × days
max(1,044.55 × 1, 784.15 × 2) = 1,568.3 Wh - Usable capacity with safety margin:
needed Wh × (1 + margin)
1,568.3 × (1 + 0.2) = 1,881.96 Wh - Rated (advertised) capacity to look for:
usable Wh ÷ (depth of discharge × (1 − derate))
1,881.96 ÷ (0.9 × (1 − 0)) = 2,091.07 Wh - Inverter continuous output:
AC running W (everything on at once); recommended = AC W ÷ 0.8 headroom
181 W; 181 ÷ 0.8 = at least 181 W, ideally 227 W (rounded up) - Inverter surge (peak) output:
AC running W + largest single extra start-up W
181 + 0 (no start-up watts entered) = at least 181 W - Solar panel to replace a day's use in one day:
daily Wh ÷ (peak sun hours × solar factor)
1,044.55 ÷ (1.86 × 0.7) = 802 W of panels, and a solar input at least that high
Result: look for at least 2,092 Wh rated capacity (2,000 Wh and over), at least 181 W continuous AC output (ideally 227 W) and 181 W surge. To replace a whole day's use from solar in one October day you'd need about 803 W of panels and a solar input at least that high.
Default assumptions and where they come from
All defaults live in one data file, with a source or reason for each. Where we couldn't find a published figure we say it's a rough estimate.
| Setting | Default | Why |
|---|---|---|
| Inverter efficiency (AC) | 90% | Rough estimate. EcoFlow's worked examples use 90% inverter efficiency as a planning assumption. Jackery and EcoFlow's quick formulas use a single 0.85 factor (Jackery's newer FAQ 0.8) covering all losses. 90% here combined with the 90% LiFePO4 usable depth of discharge gives an overall factor of 0.81, between those two quick-formula factors. It is not a measured figure for any product. [1] [2] [3] [4] |
| DC/USB conversion efficiency | 95% | Rough estimate. DC and USB outputs skip the inverter but still pass through a voltage converter, so we assume a smaller loss than AC. 95% is our planning estimate, not a published figure. Adjust it if your manufacturer gives one. |
| Usable depth of discharge, LiFePO4 | 90% | Rough estimate. EcoFlow's depth-of-discharge article gives 70–90% for lithium-ion and LiFePO4 batteries, with 80% recommended for its LiFePO4 DELTA Pro. Its 100Ah worked example uses 100% for LiFePO4, and Dometic says lithium iron phosphate batteries are "nearly 100%" usable. BLUETTI's Elite 100 V2 manual uses 90% in its operation-time formula ("DoD (Depth of Discharge) is 90%"). We use 90%, a planning estimate within that spread. It's at the top of EcoFlow's 70–90% range, so it isn't a cautious figure: lower it if you want more margin. [1] [2] [3] [4] |
| Usable depth of discharge, NMC lithium-ion | 80% | EcoFlow gives a recommended depth of discharge of up to 80% for (non-LiFePO4) lithium-ion batteries. [1] [2] |
| Temperature and ageing derate | 0% | Rough estimate. Off by default. EcoFlow says there is no fixed winter penalty and treats cold and age as planning factors (its example uses 0.95 for age and 0.90 for cold). Add a derate if the battery is old or cold. [1] [2] |
| Solar factor (share of panel rating delivered) | 70% | Rough estimate. Panels rarely deliver their rated watts: Jackery lists light intensity, angle, temperature, cables and charge-controller conversion as causes. 70% of rated watts at peak-sun equivalent is our planning estimate; Jackery does not publish a single figure. [1] |
| Inverter headroom warning | above 80% of continuous rating | Rough estimate. We show a warning (not a fail) when running AC load is above 80% of the continuous rating, to leave headroom for loads that vary. A cautious rule of thumb, not a manufacturer requirement. |
| Start-up check method | running W + largest single extra start-up | Peak demand = all running watts + the single largest extra start-up watts (start-up W − running W), because appliances rarely start at the same moment. If several motor loads may start together, add their start-ups yourself. [1] [2] [3] |
| Car-style 12 V socket limit | 10 A (about 120–126 W) | The car-style 12 V socket on each of the four power stations we checked (one per major brand) is rated 10 A: 12 V × 10 A = 120 W (EcoFlow states 12.6 V, 126 W). This is what those four spec sheets say, not a rule for every model: check yours. USB-C ports have their own limits: check each port's rating on the maker's spec sheet. [1] [2] [3] [4] |
| Safety margin (sizing calculator) | 20% on top of the energy you need | Rough estimate. Sizing adds 20% on top of the energy you need, to allow for battery ageing, cold, appliances that draw more than expected and the power station's own standby use (BLUETTI's runtime formula adds the unit's self-consumption, about 10 W for the Elite 100 V2). 20% is our planning choice, not a published figure. [1] |
| Days without recharging (sizing calculator) | 1 day | Rough estimate. One day without recharging unless you change it. |
Typical appliance wattages (check your own label)
These are typical ranges from published sources, not measurements of your appliance. The calculator fills in the upper end of each range so the estimate errs on the cautious side. Your appliance's rating plate, charger or manual is always the better figure.
| Appliance | Type | Typical | Notes and source |
|---|---|---|---|
| Fridge (mains) | AC | 40–120 W; start-up about 480 W (4 × running) | Pre-filled with the upper end of the typical range (cautious for runtime and inverter checks). Fridges switch on and off, so they don't draw this all day. For daily energy, use the kWh/year on the energy label: average watts = kWh/year × 1,000 ÷ 8,760, run for 24 hours. Start-up pre-filled at 4 × running watts: BLUETTI's manual says motors and compressors may start at 2–4 times rated power (EcoFlow says 2–3 times), so we use the cautious end. A US generator guide (Honda) estimates about 1,200 W starting for a fridge or freezer. Check your fridge's manual if it lists a start-up figure. Source · start-up source · EcoFlow blog · Honda Power Equipment (US) generator wattage estimation guide |
| Fridge-freezer (mains) | AC | 200–400 W; start-up about 1,600 W (4 × running) | Pre-filled with the upper end of the typical range (cautious for runtime and inverter checks). Cycles on and off like a fridge; see the energy label tip for daily energy. Start-up pre-filled at 4 × running watts: BLUETTI's manual says motors and compressors may start at 2–4 times rated power (EcoFlow says 2–3 times), so we use the cautious end. A US generator guide (Honda) estimates about 1,200 W starting for a fridge or freezer. Check your fridge's manual if it lists a start-up figure. Source · start-up source · EcoFlow blog · Honda Power Equipment (US) generator wattage estimation guide |
| 12 V compressor cool box | DC/USB | about 9.12 W | One manufacturer's figure for one model (Dometic CFX5 45: 0.76 Ah/h × 12 V ≈ 9.12 W) at 32 °C ambient with 4 °C inside. Your model and conditions will differ; this is already an average, so use 24 hours. Source |
| Laptop (mains charger) | AC | 20–65 W | Pre-filled with the upper end of the typical range (cautious for runtime and inverter checks). Check the watts printed on your charger. Many laptops can also charge from USB-C (DC), which avoids inverter losses. Source |
| Phone charging (USB) | DC/USB | 2.5–5 W | Pre-filled with the upper end of the typical range (cautious for runtime and inverter checks). Fast chargers can draw more while charging quickly. Source |
| Tablet charging (USB) | DC/USB | 10 W | Energy Savers lists 10 W. Source |
| Broadband router | AC | 7–10 W | Pre-filled with the upper end of the typical range (cautious for runtime and inverter checks). In a power cut your broadband may still be down if the street cabinet has no power. Source |
| LED bulb or lamp | AC | 4.3–13 W | Philips CorePro A60 bulbs (Signify UK product data): 4.3 W (470 lm, like an old 40 W bulb), 8 W (806 lm, like 60 W), 13 W (1,521 lm, like 100 W). Pre-filled with the upper end. The watts are printed on your bulb. Source · source 2 · source 3 |
| LCD TV | AC | 125–200 W | Pre-filled with the upper end of the typical range (cautious for runtime and inverter checks). Newer, smaller TVs often use less; check the label or the energy label. Source |
| Electric blanket | AC | 130–200 W | Pre-filled with the upper end of the typical range (cautious for runtime and inverter checks). Most have lower settings that use less. Source |
| CPAP machine (ResMed AirSense 11) | AC | 56.1–73.2 W | ResMed's own user guide gives typical 56.1 W and peak 73.2 W for the AirSense 11. Heated tubing and humidifier settings change it. If you rely on a medical device, ask your supplier about backup power; don't rely on this estimate. Source |
| Diesel heater (12 V) | DC/USB | 14–29 W | Pre-filled with the upper end of the typical range (cautious for runtime and inverter checks). One model's published running range (Webasto Air Top 2000 STC). The glow plug draws more for a short time at start-up and shut-down; check your heater's manual. Source |
| Starlink (Standard kit) | AC | 75–100 W | Pre-filled with the upper end of the typical range (cautious for runtime and inverter checks). Starlink's published average for the Standard kit. Other kits differ. Source |
| Desktop computer | AC | 80–200 W | Pre-filled with the upper end of the typical range (cautious for runtime and inverter checks). Source |
| Microwave | AC | 600–1,500 W | Pre-filled with the upper end of the typical range (cautious for runtime and inverter checks). The watts on the front are usually cooking power; the power drawn from the socket is higher (Honda's guide lists about 1,000 W for a 650 W microwave). Check the rating plate. Source |
| Kettle | AC | 3,000 W | Most UK kettles are 2,000–3,000 W, more than many portable power stations' continuous rating. Check the rating plate. Source |
| Hairdryer | AC | 2,000 W | High-power heater: check the rating plate. Source |
Frequently asked questions
What size power station do I need for camping?
For a weekend with a 12 V cool box, phones and a lamp, our example scenario comes to about 766 Wh rated capacity. A cool box dominates the total, so check its stated consumption. See power station for camping.
What size power station do I need for a campervan?
It depends on heating, fridge and devices like Starlink. Our van weekend example needs about 2,092 Wh with a 200 W roof panel in October, or about 2,786 Wh with no solar. See power station for a campervan.
Can a power station run a microwave?
Only if its continuous AC output covers the microwave's input watts (on the rating label; the Camping and Caravanning Club says an 800 W microwave's input, "particularly on start-up, may be up to twice this" (C&CC)) and its surge rating covers the start-up. Enter the label figure in the tool.
Is the result exact?
No. It's a planning estimate based on published specs and labelled assumptions. Cold and older batteries deliver less. You can change every assumption.
Do you recommend a model?
No. We don't rank or recommend. The spec table lists models alphabetically with their stated figures so you can compare.
Why is the rated capacity bigger than the energy I use?
Power stations don't let you use every watt-hour on the label, the inverter loses some energy turning battery power into mains power, and batteries lose capacity with age and cold. The calculator adds those back, plus a safety margin, so the advertised (rated) figure you compare is big enough.
What if my appliance has a start-up surge?
Fridges, freezers, pumps and other motors can briefly need several times their running watts. Enter the start-up watts from the label or manual if you know them. The calculator adds the largest single start-up surge to everything else running, which is what the inverter's surge rating has to cover.
Is this a recommendation to buy a particular model?
No. The calculator gives the specs to look for. Compare models on their manufacturers' published capacity, continuous output, surge output and solar input.
Related: Runtime calculator · Methodology · Power station safety
Sources
- Jackery blog: What can a Jackery Explorer 1000 Plus run? (formula: capacity in Wh × 0.85 ÷ operating wattage, "calculated considering 85% efficiency")
- Jackery FAQ: How can I estimate the runtime of my portable power station? (formula: Wh × 0.8 ÷ device W; not suitable for fridges and other start-up loads)
- EcoFlow Ireland FAQ: How do I estimate runtime? (Wh × 0.85 ÷ device W)
- EcoFlow blog: How long does a 100Ah lithium battery last? (DoD, 90% inverter efficiency example)
- EcoFlow blog: What is depth of discharge for batteries? (lithium-ion up to 80%; DELTA Pro LiFePO4 recommended 80%)
- EcoFlow blog: How to estimate DELTA Pro Ultra X runtime (SOC window × remaining capacity × temperature × efficiency; 0.90 planning assumptions)
- EcoFlow blog: Do portable power stations work in cold weather? (usable capacity factor; no fixed winter penalty)
- Jackery: Charging power loss (why panels deliver less than their rated watts)
- European Commission JRC, PVGIS monthly radiation (MRcalc), PVGIS-SARAH3, 2014–2023; daily values calculated by us from monthly totals
- Energy Savers (Centre for Sustainable Energy): How much electricity am I using? (typical power ratings and ranges)
- Centre for Sustainable Energy: How much electricity am I using? (average power ratings)
- Honda Power Equipment (US) generator wattage estimation guide: approximate starting and running watts (US generator guide estimate)
- Home generator systems wattage worksheet, archived copy (Wayback Machine, 8 Sep 2024): total running watts + the single highest additional surge ("you will only need to factor in the appliance with the highest additional surge watts")
- Webasto Air Top 2000 STC specifications (power consumption 14–29 W)
- Starlink Standard kit specification sheet (average power consumption 75–100 W)
- Energy Saving Trust: energy saving light bulbs (lumens, not watts, measure brightness)
- ResMed AirSense 11 user guide (ResMed, official PDF), technical specifications: typical power consumption 56.1 W, peak 73.2 W
- Signify (Philips) CorePro LEDbulb 4.3-40W A60 E27, UK product data: 470 lm, power consumption 4.3 W
- Signify (Philips) CorePro LEDbulb 8-60W A60 E27, UK product data: 806 lm, power consumption 8 W
- Signify (Philips) CorePro LEDbulb 13-100W A60 E27, UK product data: 1,521 lm, power consumption 13 W
- BLUETTI Elite 100 V2 user manual (EU), FAQ: operation time uses "DoD (Depth of Discharge) is 90%" and inverter efficiency "over 90%"; devices with motors or compressors may start at 2–4 times their rated power; operation time includes self-consumption of about 10 W; specifications: Cigarette Lighter Port 12V / 10A
- EcoFlow blog: How many watts does a refrigerator use? (start-up surge typically 2–3 times running watts)
- EcoFlow UK: RIVER 3 specs, Car Output 12.6V, 10A, 126W max (checked 18 Oct 2026)
- Jackery Explorer 1000 v2 user manual (230 V version), Car Port 12V⎓10A (checked 18 Oct 2026)
- Anker SOLIX UK: C1000 specs, Car Auxiliary 1× 12V⎓10A (checked 18 Oct 2026)
- Dometic UK: CFX5 45, Energy Consumption 12VDC (Ambient@32C, Internal@4C) 0.76 Ah/h (checked 18 Oct 2026)
- Dometic CFX3 45 product FAQ (usable capacity: lithium NMC "roughly 80%", lithium iron phosphate "nearly 100%")
- BLUETTI UK: AC180 product page (12V DC Outlet: "1 × 12V/10A (Car outlet, regulated.)")
- Jackery UK: Explorer 1000 v2 product page
Figures last checked: 18 October 2026.