RV Inverter Calculator

Check the appliances you run on AC — get the right inverter size and whether you need pure sine or modified sine.

Check the appliances you need to run on AC power

Toggle each appliance on or off. Edit watts and surge power as needed.

Appliance	Watts	Surge W	Use?
Microwave
Coffee Maker
Hair Dryer
Laptop / Work
TV / Monitor
Phone Charger
Power Tool (drill)
CPAP Machine
Electric Kettle
Space Heater

Recommended inverter size

3,000W Pure sine wave

Total continuous load2,265 W

Largest surge load1,800 W

Inverter minimum size2,900 W

Battery draw at 12V223 A

Inverter type neededPure sine wave

You have sensitive electronics (laptop, CPAP, phone). A pure sine wave inverter is required to avoid damage or erratic behavior.

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How to Use This Calculator

Check the appliances you run on AC power

Toggle each appliance you actually use in your RV or van. The calculator distinguishes between continuous watts (what an appliance draws while running) and surge watts (the brief spike when it starts). Motors — like in a microwave's turntable, hair dryer, or power tool — draw 1.5–3x their rated wattage for a fraction of a second on startup. Your inverter must handle the surge, not just the continuous load.

Edit watts and surge values

Default values are typical averages, but your appliances may vary. Check the label or manual for the wattage rating. For appliances without a clear surge rating, a good rule of thumb: resistive loads (heaters, kettles, incandescent bulbs) have no surge — set surge = watts. Motor loads (drills, blenders, AC units) have surge = 2–3x watts.

Interpret the recommendation

The calculator outputs the minimum inverter continuous watt rating and whether you need a pure sine wave or can use modified sine. It also shows the battery amperage draw at 12V — critical for knowing how quickly you'll drain your bank when running AC loads.

The Formula

Total continuous load = Sum of watts for all active appliances Inverter minimum (by load) = Total continuous × 1.25 safety buffer Inverter minimum (by surge) = Largest single surge load × 1.20 Recommended inverter = Max of both minimums, rounded to next standard size Battery draw (A) = Total continuous ÷ 12V ÷ 0.85 (inverter efficiency)

The 25% safety buffer on continuous load accounts for inverter heat derating at high ambient temperatures (common in vehicles in summer). Running an inverter at 80% of rated capacity keeps it cool and extends its life. The 85% inverter efficiency figure is typical for quality pure sine wave inverters; cheap modified sine units may be only 75-80% efficient.

Example

Jamie — Full-timer with home office and hair dryer

Jamie runs a laptop (65W), TV (80W), phone charger (20W), microwave (1,200W surge 1,800W), coffee maker (900W), and uses a hair dryer (1,500W surge 1,800W) in the morning.

Total continuous load3,765 W

Largest surge1,800 W (hair dryer)

Continuous × 1.254,706 W

Result

Recommended inverter5,000W pure sine

Inverter typePure sine wave (has laptop)

Battery draw @ 12V~370 A

Running hair dryer + coffee maker simultaneously at 12V draws 370 amps — that's extremely demanding on a 12V battery bank and wiring. In practice, Jamie would stagger these loads or consider a 24V or 48V system for higher AC power use, which significantly reduces cable size and heat.

FAQ

Pure sine wave vs modified sine wave inverter — which do I need? ▼

Pure sine wave produces clean AC power identical to the grid. Required for: laptops, CPAP machines, TVs, audio equipment, variable-speed appliances, and anything with a microprocessor. Running these on modified sine can cause overheating, buzzing, reduced efficiency, or permanent damage.

Modified sine wave is cheaper and works fine for simple resistive loads: incandescent bulbs, basic power tools, coffee makers, and phone chargers (though may charge slower). If you have a laptop or CPAP, spend the extra $50-100 for pure sine.

What size inverter do I need for an RV microwave? ▼

A 900W RV microwave typically draws 1,200-1,500W from the inverter (microwaves are about 60-65% efficient). Include the 1.5x surge for the turntable motor. A 1,500W pure sine inverter comfortably runs the microwave alone. If you also run the coffee maker (900W) at the same time, you need a 2,000-2,500W inverter. Most RV full-timers find a 2,000W inverter the sweet spot.

Why does my inverter get so hot? ▼

Inverters convert DC to AC at 85-95% efficiency, meaning 5-15% of power becomes heat. At 2,000W load, a 90% efficient inverter generates 200W of heat — about the same as a small light bulb. Heat problems occur when: (1) the inverter is sized too small and running near 100% capacity continuously, (2) there's poor ventilation around the inverter, or (3) ambient temperature is high (like a van in summer). Size your inverter at 20-25% above maximum load and ensure at least 6 inches of clearance around it.

Can I run a hair dryer in an RV on solar? ▼

Yes, but it's battery-intensive. A 1,500W hair dryer running 10 minutes uses 250 Wh — roughly what a full-timer uses for lights, fan, and phone all day. At 12V, it draws about 150 amps from your battery bank. This is manageable with a good lithium bank (200Ah+). Use it in the morning when solar production is picking up. If you use a hair dryer daily, factor 250-500 Wh into your daily load calculation.

What inverter brand is best for RVs? ▼

For pure sine wave: Victron Multiplus (premium, has built-in charger, ideal for lithium), Renogy 2000W (good value, popular in van builds), Giandel 2200W (budget-friendly with decent quality). Avoid very cheap no-brand inverters — they frequently over-rate wattage and have poor waveform quality. For a full-time setup, spend at least $150-300 for a quality 2,000W unit. The Victron Multiplus (with pass-through and built-in charger) is the gold standard for serious RV builds.