What size inverter do I need for a refrigerator and AC?

A refrigerator (150W run, 600W surge) + 1-ton AC (1,200W run, 3,600W surge) + typical electronics = about 1,500W continuous and 3,900W peak surge. You'd need a 2,000W inverter with a 4,000W surge rating minimum.

How do I calculate inverter surge watts needed?

Add all running watts together, then find the appliance with the biggest difference between surge and running watts. Add that delta to your total running load. This gives the worst-case peak surge when that motor starts while everything else is already running.

Should I get pure sine wave or modified sine wave?

Pure sine wave is recommended for all modern appliances — refrigerators, AC units, electronics, and anything with a variable-speed motor. Modified sine wave can damage motors, cause buzzing in audio, and won't work with some electronics. The price difference is typically $30-60 on a quality inverter.

Inverter Load Calculator

Check your appliances, enter running and surge watts — get your total load and recommended inverter size.

How to Use This Calculator

Check the appliances you want to run

The calculator starts with a list of common appliances. Check the ones you plan to run simultaneously — not just occasionally, but at the same time. The inverter must handle the full combined load of everything running at once, plus starting surges.

Edit running and surge watts

Each appliance has two wattage fields: running watts (the steady-state power draw) and surge watts (the momentary peak when a motor starts). For resistive loads like lights, kettles, and heaters, running watts equal surge watts. For motor loads — refrigerators, air conditioners, washing machines, pumps — surge can be 3–8× the running watts. Check the appliance label or use the defaults as a starting point.

Add custom appliances

Use the custom appliance form at the bottom to add any load not in the default list. You only need the running watts if you don't know the surge — the calculator will use running watts for both.

Understand the result

The calculator outputs the total continuous load (everything running at once), the peak surge load (the worst-case moment when the biggest motor starts), and the recommended inverter size — the next standard size above your continuous load with a 20% safety margin.

The Formula

Total continuous load = sum of (running watts × quantity) for all checked appliances Peak surge = total continuous − highest-surge appliance running watts + highest-surge appliance surge watts Sized continuous = total continuous × 1.20 (20% safety margin) Recommended inverter = next standard size ≥ sized continuous AND handles peak surge

The key insight on surge: you don't add up all the surge watts simultaneously — only one motor starts at a time. The worst case is when your largest motor-load appliance starts while everything else is already running. That's why the formula takes the total running load and adds the single biggest surge delta, not all surge watts combined.

The 20% safety margin on continuous load protects against: (1) appliances drawing more than their rated watts at end of life, (2) power factor issues with some electronic loads, and (3) inverter derating at high ambient temperatures. Running an inverter at 100% capacity shortens its life significantly.

Example

Weekend cabin backup power setup

A cabin owner wants to run a refrigerator, LED TV, laptop, and a window AC unit on an inverter during power outages.

Refrigerator150W run / 600W surge

LED TV (50")80W run / 80W surge

Laptop65W run / 65W surge

Window AC (1 ton)1,200W run / 3,600W surge

Result

Total continuous load1,495W

Peak surge (AC starting)1,495 − 1,200 + 3,600 = 3,895W

Sized with 20% margin1,794W continuous

Recommended inverter2,000W, 4,000W+ surge rated

A 2,000W pure sine wave inverter with a 4,000W surge rating handles this load. The AC's surge is the critical spec — many cheap 2,000W inverters only have 2,500W surge ratings and will shut down when the AC starts. Always check the inverter's surge specification, not just its continuous rating.

FAQ

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

Pure sine wave is the safe choice for all appliances. It produces clean AC power identical to grid power. Required for: sensitive electronics (medical equipment, variable speed motors), AC motors (refrigerators, air conditioners, pumps), power tools, and most modern appliances. Modified sine wave is cheaper but can cause overheating in motors, buzz in audio equipment, incorrect readings in some digital clocks, and may not work with some electronics. If you're investing in a proper off-grid or backup system, buy pure sine wave — the cost difference on a quality inverter is typically $30–60 and it's always worth it.

How do I find the surge watts for my appliances? ▼

Check the appliance label or manual for "starting current" or "LRA (locked rotor amps)." If not listed, use these rules of thumb: refrigerators and freezers: 3–4× running watts; air conditioners: 3–8× running watts; well pumps: 5–7× running watts; sump pumps: 3–5×; washing machines: 3–4×; power tools with motors: 3×. Resistive loads (lights, heaters, kettles, ovens) have no surge — their running and surge watts are equal. Electronics (TVs, computers, phone chargers) also have no meaningful surge.

What does the 20% safety margin account for? ▼

Running an inverter at its nameplate limit reduces efficiency and generates excess heat, shortening its life. The 20% margin accounts for: appliances drawing more than rated watts (common with aging appliances), power factor — some loads (motors, fluorescent lights) draw apparent power in VA that's higher than true watts, inverter derating at high temperatures (most inverters derate 10–20% above 40°C), and future load additions. Think of the 20% as buying a 2,000W inverter for a 1,600W load — it runs cooler, lasts longer, and gives you room to add loads.

Can I run an air conditioner on a solar inverter? ▼

Yes, but air conditioners are the most demanding load in any solar system — both in terms of peak surge watts and continuous power consumption. A 1-ton (12,000 BTU) AC uses 900–1,400W continuously and surges to 2,800–4,500W at startup. You need: an inverter sized for 3–5× the AC's running watts for surge capacity, enough solar panels (typically 1.5–3× the AC wattage), and either a large battery bank or the ability to run the AC only when the sun is strong. Mini-split systems are much more efficient (COP 3–4) and surge much less than window units — a better choice for off-grid AC.