Power station sizing: Wh vs watts (UK)
Two numbers matter: Wh (how long it lasts) and W (what it can run). Here’s how to size without overpaying.
- Wh = stored energy (runtime)
- W = output power (what you can run at once)
- Planning: usable Wh is often ~80–90% of the label
Jump to what you need
3 common sizing scenarios
PCRUse these as a starting point, then plug your real numbers into the formula.
Buying a power station and confused by the specs? You are not alone.
This guide explains the two numbers that actually matter — Wh (watt-hours) and W (watts) — so you can pick the right size without overspending.
The short version
- Wh (watt-hours) = how much energy is stored (like the size of a fuel tank)
- W (watts) = how fast energy flows out (like the width of the fuel pipe)
You need enough Wh to last the duration, and enough W to run your devices without tripping.
Wh (watt-hours): how long it lasts
Watt-hours tell you total capacity.
Simple formula:
Runtime (hours) ≈ (Wh × 0.8) ÷ device watts
The 0.8 accounts for inverter losses (energy lost as heat).
Example
- Power station: 500Wh
- Router: 15W
Runtime ≈ (500 × 0.8) ÷ 15 = 26 hours
Quick reference (approximate runtimes from 500Wh)
| Device | Watts (typ.) | Runtime (rough) |
|---|---|---|
| Wi‑Fi router | 10–15W | 25–40 hours |
| Phone charging | 10–20W | 20–40 charges |
| Laptop | 30–60W | 6–13 hours |
| LED lamp | 5–10W | 40–80 hours |
| Mini fridge | 50–80W avg | 5–8 hours |
W (watts): what you can run
Watts tell you the maximum load the power station can handle at once.
Look for two ratings: - Continuous (or rated) watts — what it can run steadily - Surge (or peak) watts — short bursts for startup spikes
Why surge matters
Some devices (fridges, power tools) draw a big spike when they start. If your power station cannot handle the surge, it trips — even if the battery is full.
Rule of thumb for fridges: - Running: 50–150W - Startup surge: 3–7× that (so 150–1000W briefly)
If you want to run a fridge, aim for 1000W+ continuous and 2000W+ surge.
Common mistakes
1. Buying on Wh alone
A 1000Wh station with only 300W output will not run a fridge. Capacity is not everything.
2. Ignoring inverter efficiency
You never get 100% of the rated Wh. Expect 80–90%. Budget accordingly.
3. Running too many things at once
Adding devices adds watts. A router (15W) + laptop (50W) + lamp (10W) = 75W. Fine on most stations. Add a kettle (2000W)? Good luck.
How to size for your setup
Step 1: List your devices
Write down what you want to run and their wattage. (Check the label or manual.)
Step 2: Add up the watts
Total watts = what continuous output you need.
Step 3: Estimate runtime
Decide how many hours you need backup for, then:
Wh needed ≈ (total watts × hours) ÷ 0.8
Example
- Router (15W) + lamp (10W) + phone charging (15W) = 40W
- Want 12 hours runtime
- Wh needed ≈ (40 × 12) ÷ 0.8 = 600Wh
A 500–700Wh power station would be a sensible choice.
Quick sizing guide
| Use case | Min capacity | Min output |
|---|---|---|
| Router + phones + lights (overnight) | 300–500Wh | 200W |
| Above + laptop (full day) | 500–800Wh | 300W |
| Above + mini fridge (sometimes) | 1000Wh+ | 1000W (aim ~2000W surge) |
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