What Size Inverter for a Campervan? (Sizing Guide)
Picking the right size inverter means balancing two things: having enough power for the appliances you want to run, and not paying for capacity you will never use. An oversized inverter wastes money, adds weight, and increases standby drain. An undersized one trips out when you need it most.
This guide walks you through the calculation step by step, explains what each common inverter size can power, and covers the critical battery cable sizing that most guides overlook.
If you have not already worked out your 230V appliance requirements, start with a power audit. For specific inverter recommendations after you have worked out your size, see our best inverters guide.
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Enter your 230V appliances into our free calculator. It recommends the correct inverter size, cable gauge, and fuse rating automatically.
The Sizing Calculation
Step 1: List Your 230V Appliances
Write down every appliance you plan to run through the inverter. Only include 230V devices — anything running on 12V DC does not need the inverter.
Step 2: Find Each Appliance's Wattage
Check the label or manual for the wattage. Use the input power (not the output power). For a microwave rated at "800W cooking power," the input power is typically 1,200-1,300W.
Step 3: Identify Your Peak Simultaneous Load
You rarely run every appliance at once. Work out the realistic maximum — the highest total wattage you would draw at any single moment.
For example:
| Appliance | Watts |
|---|---|
| Laptop charger | 65W |
| Phone charger (x2) | 30W |
| LED TV | 50W |
| Hair straighteners | 200W |
| Peak simultaneous load | 345W |
Step 4: Add a 20% Safety Margin
Multiply your peak load by 1.2 to account for:
- Slight variations in actual power draw
- Inverter efficiency losses
- Motor start-up surges on some devices
345W x 1.2 = 414W — a 500W or 800W inverter would work comfortably.
Step 5: Check for Surge Requirements
Some appliances — particularly those with motors or compressors — draw a large surge of power when they first start up. This surge can be 2-5 times the running wattage and lasts less than a second. Your inverter must handle this surge without shutting down.
Inverter specs list both continuous and peak/surge ratings. The peak rating is what matters for motor start-up.
Most surge concerns are overstated
In practice, the only common campervan appliance with a significant start-up surge is a compressor fridge running on 230V (which you should not be doing — use a 12V compressor fridge instead). Laptops, chargers, microwaves, and most small appliances do not have meaningful surge requirements.
Common Inverter Sizes and What They Power
300W Inverter
| Can Power | Cannot Power |
|---|---|
| Laptop charger | Hairdryer |
| Phone/tablet chargers | Microwave |
| Electric shaver | Kettle |
| Small LED TV | Hair straighteners |
| Camera battery charger | Toaster |
Best for: Minimalist builds where 230V is only needed for charging electronics. Weekend vans, motorcycle/bicycle touring vehicles.
Typical price: £60-£120
800W Inverter
| Can Power | Cannot Power |
|---|---|
| Everything above | Microwave (most models) |
| Hair straighteners (up to 200W) | Induction hob |
| Small travel hairdryer (up to 700W) | Full-size kettle |
| Blender/food processor | Toaster |
| Gaming console | Electric heater |
Best for: The most popular choice for UK campervans. Covers the vast majority of needs for weekend, holiday, and even many full-time builds. The Victron Phoenix 800 sits in this category.
Typical price: £130-£240
1,500W Inverter
| Can Power | Cannot Power |
|---|---|
| Everything above | Full-size kettle (3kW) |
| Low-wattage microwave (700-800W cooking) | Large induction hob |
| Small induction hob (single ring, low setting) | Electric heater (most models) |
| Hair dryer (most models) | Washer/dryer |
| Travel kettle (low wattage) |
Best for: Builders who want to run a microwave or occasional higher-power appliances. Full-time vanlifers who want more flexibility.
Typical price: £100-£300
2,000W Inverter
| Can Power | Cannot Power |
|---|---|
| Everything above | Full-size kettle (3kW) |
| Single-ring induction hob (most settings) | Full-size oven |
| Larger microwave | Washer/dryer (large) |
| 2kW hair dryer | Electric shower |
| Travel kettle |
Best for: Builds focused on electric cooking. Large vans with big battery banks. Full-time vanlifers who have moved away from gas.
Typical price: £200-£500
3,000W Inverter
At this level, you can run almost any single domestic appliance, including full-power induction hobs and high-wattage kettles. However, the battery demands are enormous — a 3,000W inverter at full load draws approximately 275A from a 12V battery system.
Best for: Truck conversions and large builds with 24V systems and massive battery banks (400Ah+). Rarely practical for standard campervans.
Typical price: £350-£800+
Continuous vs Peak Ratings: What Matters
Every inverter has two ratings:
- Continuous (rated) power: What it can deliver indefinitely. This is the number that matters for sizing.
- Peak (surge) power: What it can handle for a few seconds. Usually 1.5-2x the continuous rating. This handles motor start-up surges.
When we say "800W inverter," we mean 800W continuous. Its peak rating might be 1,500W, meaning it can handle a brief 1,500W surge when a motor starts.
Do not size based on peak ratings
Some cheaper inverters advertise their peak rating prominently (e.g., "2000W inverter!" which is actually 1,000W continuous). Always check the continuous rating — that is the number you need to match to your peak simultaneous load.
Battery Cable Sizing for Inverters
This is the part many guides skip, and it is critically important. Inverters draw very high current from the 12V battery. The cables between your battery and inverter must be thick enough to handle this current safely.
Why It Matters
At 12V, current is roughly 10x what you might expect from a 230V perspective. An 800W inverter at full load draws:
800W / 12V / 0.93 (efficiency) = ~72A
A 2,000W inverter draws approximately 185A at full load. That is serious current.
Cable Sizing Table
| Inverter Size | Max Current Draw | Cable Size (up to 1m) | Cable Size (1-2m) | Fuse Size |
|---|---|---|---|---|
| 300W | ~30A | 10mm² | 16mm² | 40A |
| 800W | ~75A | 25mm² | 35mm² | 100A |
| 1,500W | ~140A | 35mm² | 50mm² | 175A |
| 2,000W | ~185A | 50mm² | 70mm² | 225A |
| 3,000W | ~275A | 70mm² | 95mm² | 300A |
These figures assume copper cable and a maximum 3% voltage drop.
Fusing
An appropriately rated fuse (ANL or MEGA type for high currents) must be installed on the positive cable as close to the battery terminal as possible. The fuse protects against cable faults — without it, a short circuit could cause the cable to catch fire.
Undersized cables cause fires
Undersized battery-to-inverter cables are one of the most dangerous mistakes in a campervan build. The cable heats up, the insulation melts, and the exposed conductor can short against the van's metalwork. Always use the correct cable cross-section for your inverter's maximum current draw and the cable run length. If in doubt, go one size up.
The Battery Size Connection
A larger inverter needs a larger battery bank to be useful. There is no point installing a 2,000W inverter if your battery cannot sustain the load.
A rough guide to minimum usable battery capacity (LiFePO4) for each inverter size:
| Inverter Size | Minimum Battery | Reasoning |
|---|---|---|
| 300W | 50Ah | 30A draw is fine for any LiFePO4 |
| 800W | 100Ah | 75A draw is within 1C for 100Ah |
| 1,500W | 200Ah | 140A draw needs headroom |
| 2,000W | 200-300Ah | 185A draw — check battery max discharge rate |
| 3,000W | 400Ah+ | 275A draw — most batteries need paralleling |
For battery sizing guidance, see our battery capacity guide.
Common Sizing Mistakes
1. Sizing for Everything at Once
You do not need an inverter that can run every 230V appliance simultaneously. Size for your realistic peak — the most you would actually use at the same moment. Running a microwave while using a hairdryer while charging a laptop is not a realistic scenario.
2. Forgetting Inverter Efficiency
An 800W inverter delivering 800W to your appliance is drawing roughly 860-890W from the battery (accounting for the inverter's own efficiency loss). This matters for battery drain calculations but does not affect inverter sizing — the rated output is what counts.
3. Ignoring Standby Drain
A 2,000W inverter left on standby all day at 15W consumes 360Wh — for nothing. If your actual usage is mostly low-power (laptop charging), a smaller inverter with lower standby drain may be more practical overall.
4. Buying Too Large "Just in Case"
Bigger is not always better. A larger inverter has higher standby drain, weighs more, costs more, and needs thicker (more expensive) cables. Buy for your actual needs with a 20% margin, not for hypothetical future requirements.
FAQ
What size inverter do I need for a laptop?
A typical laptop charger draws 45-100W. A 300W inverter is more than sufficient. Even if you charge two laptops simultaneously, 300W covers it. However, most builds choose an 800W inverter for versatility, as you will likely want to power other 230V devices too.
Can I run a kettle from an inverter?
A standard UK kettle draws 2,200-3,000W — far more than most campervan inverters can handle. Travel kettles are available at 600-1,000W, which work with 800W+ inverters (check the specific wattage). Alternatively, use a 12V kettle or heat water on a gas hob.
What size inverter for a coffee machine?
Drip filter machines draw 600-1,000W. Pod machines (Nespresso, Dolce Gusto) draw 1,200-1,500W due to the heating element and pump. For a pod machine, you need a 1,500W inverter minimum. A cafetiere or AeroPress with a low-wattage kettle is a more practical off-grid solution.
Does a bigger inverter drain my battery faster?
When delivering the same power, all inverters drain the battery at a similar rate. But a bigger inverter has higher standby consumption when idle. If you leave a 2,000W inverter on all day but only use it for 30 minutes of actual power, the standby drain is the dominant cost. Size appropriately and switch off when not in use.