Solar Inverter Calculator
Figure out what size solar inverter you actually need. Add your appliances, and the calculator works out your running load, surge demand, and a recommended inverter capacity — with the reasoning shown, not just a number.
Sizing a solar inverter correctly is one of the most consequential decisions in a solar or backup power system. An inverter that's too small will trip, shut down, or fail to start high-draw appliances like refrigerators and air conditioners. One that's oversized adds unnecessary cost and, in some off-grid setups, runs less efficiently at low loads. What size solar inverter do I need? is one of the most common questions homeowners ask before buying equipment — and the honest answer depends on your specific appliances, how many run at once, and how much surge power your equipment needs to start.
This solar inverter calculator estimates your required inverter capacity, maximum running load, starting/surge power, and a recommended inverter size based on the appliances you enter. It also walks through solar array sizing, battery voltage considerations, and a practical safety margin — so you leave with numbers you understand, not a black box.
Build Your Appliance Load List
Add every appliance you want the inverter to power. Pick a preset to auto-fill typical wattage, or choose "Other / custom load" and enter your own numbers from an appliance nameplate.
Your Estimated Inverter Sizing
Based on a required capacity of 0 W, rounded up to a practical, commonly available inverter class.
This is an educational estimate. Confirm your final choice against the inverter's continuous power rating, surge rating, battery voltage, PV input limits, and local electrical code before purchasing or installing.
How the Inverter Sizing Calculation Works
The math behind inverter sizing is straightforward once you separate two different kinds of demand: the power your appliances draw while running normally, and the extra power some of them need for a brief moment when they start.
Total Running Load
Total Running Load = Sum of Running Watts for every appliance operating at the same time. If you run a refrigerator (150 W), LED lighting (60 W), a Wi-Fi router (15 W), and a TV (100 W) simultaneously, your running load is 325 W.
Starting / Surge Power
Motor-driven appliances — refrigerators, freezers, water pumps, air conditioners, washing machines — briefly draw significantly more power than their running wattage when the compressor or motor first engages. A refrigerator that runs at 150 W might momentarily need 300–450 W to start. If your inverter can't supply that brief surge, the appliance may fail to start or the inverter may fault out. The calculator estimates surge demand by taking the largest individual surge draw among your appliances and adding it on top of the running load of everything else, since it's uncommon (though not impossible) for every motor to start at the exact same instant.
Required Inverter Capacity
Required Inverter Capacity = Maximum Expected Load × (1 + Safety Margin). The "maximum expected load" is whichever is higher: your total running load, or your estimated surge scenario. A 20–25% safety margin is then applied to account for inverter efficiency losses, temperature derating, and everyday variability in how appliances actually get used.
It's worth being clear about a common misconception: simply adding up the nameplate wattage of every appliance in the house does not necessarily represent your real simultaneous load, because not everything runs at once. At the same time, ignoring surge power because "it only lasts a second" is one of the more common ways an inverter ends up undersized. Good sizing accounts for both realities rather than picking whichever number is more convenient.
Solar Panel Capacity vs. Inverter Capacity
A frequent point of confusion is assuming solar array size and inverter size should match one-to-one. A 5 kW solar array does not automatically mean you need exactly a 5 kW inverter — the two numbers describe different things and are sized against different constraints.
DC Input vs. AC Output
Solar panels produce DC (direct current) power. The inverter converts that DC power into AC (alternating current) power that household appliances and the utility grid use. The inverter's AC output rating is what determines how much continuous power it can deliver to your loads or export to the grid.
DC/AC Ratio and Clipping
Many installers intentionally size the DC array somewhat larger than the inverter's AC rating — commonly discussed as a DC/AC ratio above 1.0. This is because panels rarely produce their full rated output simultaneously due to temperature, angle, and less-than-ideal sun conditions. A moderately oversized array can help the inverter reach a fuller output earlier in the morning and later in the afternoon. The tradeoff is "clipping," where on the sunniest days the array could technically produce more DC power than the inverter is rated to convert, and the excess above the inverter's ceiling isn't used.
Maximum PV Input, MPPT Range, and Maximum PV Current
Beyond the AC rating, inverter datasheets specify a maximum PV input (the largest DC array they can safely accept), an MPPT voltage range (the voltage window across which the Maximum Power Point Tracker operates efficiently), and a maximum PV input current per MPPT channel. Solar array design has to fit within all of these limits, not just the headline AC wattage — which is why panel configuration (how many panels in series/parallel) is its own calculation, separate from choosing your household's inverter capacity.
Battery and Inverter Sizing
For off-grid and hybrid systems with battery storage, the inverter's power draw is ultimately limited by what the battery bank can safely deliver. An inverter rated higher than the battery's discharge capability won't reliably reach its full rated output in practice.
A simplified relationship used for estimation is:
Battery Power ≈ Battery Voltage × Battery Current
12V Systems
- Common in small setups, RVs, and light backup use
- Higher current needed for the same wattage vs. higher voltages
- Thicker cabling often required at higher loads
24V Systems
- Middle ground for moderate household loads
- Lower current than 12V for equivalent power
- Common in small-to-mid off-grid cabins
48V Systems
- Common for larger homes and higher-power off-grid systems
- Delivers more power at lower current, reducing cable losses
- Typically paired with larger inverter classes (3 kW+)
This is why larger home and off-grid systems commonly move to higher battery voltages: delivering several kilowatts at 12V would require very high current and correspondingly heavy, expensive cabling. In practice, real systems also lose some power to conversion inefficiency, wiring resistance, and battery internal resistance, so actual usable output is always somewhat lower than the theoretical voltage-times-current figure — and every inverter has its own maximum continuous and surge current limits regardless of what the battery could theoretically supply.
Off-Grid vs. Grid-Tied vs. Hybrid Inverters
Inverter sizing also depends on which type of system you're building, since each architecture is designed around a different relationship with the utility grid and battery storage.
Grid-Tied Inverter
- Designed to synchronize with and feed power to the utility grid
- Typically does not provide backup power during an outage unless paired with additional backup equipment
- Sizing is usually driven by array output and export limits
Off-Grid Inverter
- Operates independently from the utility grid
- Requires a properly sized battery bank to supply power at all times
- Sizing is driven almost entirely by household load and battery discharge capability
Hybrid Inverter
- Can combine solar input, battery storage, and grid connection, depending on the model
- Often supports automatic switching to battery backup during outages
- Sizing considers both grid-interactive and battery-driven operation
Choosing between these categories should come before finalizing inverter size, since it shapes which specifications matter most for your project — including whether backup power during a grid outage is actually part of the design.
How to Choose a Solar Inverter
Once you have an estimated capacity from the calculator above, comparing actual inverter models means looking past the headline wattage number. Consider each of the following, understanding that specifications vary by manufacturer and model:
- Continuous power rating — the wattage the inverter can sustain indefinitely under normal operating conditions.
- Surge power rating — the brief overload capacity available for motor startup, usually specified for a few seconds up to a couple of minutes.
- Battery voltage compatibility — matching the inverter's rated input voltage (commonly 12V, 24V, or 48V) to your battery bank.
- PV input capacity — the maximum DC array size and voltage the inverter can accept, for systems with solar charging built in.
- MPPT range and number of trackers — affects how flexibly you can configure panel strings and how well the inverter handles partial shading or mixed orientations.
- Efficiency — how much power is lost in DC-to-AC conversion; even small differences add up over years of operation.
- Pure sine wave output — important for sensitive electronics and for motors that expect clean AC power to run properly.
- Monitoring features — app or display-based visibility into real-time load, battery state, and system health.
- Warranty — coverage length and terms vary considerably between manufacturers.
- Certifications — relevant safety and grid-interconnection listings for your region.
- Grid compatibility — voltage, frequency, and interconnection standards required in your area.
- Generator compatibility — whether the inverter can accept and manage a backup generator input.
- Battery chemistry compatibility — lithium, lead-acid, and other chemistries have different charge profiles the inverter/charge controller needs to support correctly.
Example Inverter Sizing Calculations
These examples are educational estimates meant to illustrate the sizing process — your own numbers will vary based on your specific appliances and how they're actually used.
Small Apartment / Basic Backup
Running watts: LED lighting (40W), Wi-Fi router (15W), laptop (60W), TV (80W) — roughly 195W running.
Startup consideration: Minimal, since none of these are motor-driven loads with significant surge.
Safety margin: 25% applied for headroom.
Approximate inverter size: A 1 kW class inverter comfortably covers this load with room to spare.
Home With Refrigerator, Lights, Fans, TV, and Internet Equipment
Running watts: Refrigerator (150W), LED lighting (100W), ceiling fans x2 (150W), TV (100W), Wi-Fi router (15W), desktop computer (200W) — roughly 715W running.
Startup consideration: Refrigerator surge could briefly add 300–450W on top of the rest running.
Safety margin: 25%.
Approximate inverter size: A 2 kW class inverter is a reasonable estimate for this load pattern.
Larger Home With Washing Machine, Water Pump, Microwave, Computers, and Air Conditioning
Running watts: Refrigerator (150W), lighting (150W), washing machine (500W), water pump (750W), microwave (1000W), computers (300W), air conditioner (1200W running) — roughly 4,050W running when several run together.
Startup consideration: Air conditioner and water pump surge can each briefly add well over their running wattage; the largest single surge event matters more than adding every surge together.
Safety margin: 25%, sometimes higher for off-grid setups with heavy motor loads.
Approximate inverter size: A 6–8 kW class inverter is a common estimate for a load profile like this, though a professional load study is recommended before purchase.
Common Inverter Sizes and Typical Use
The table below outlines general categories seen in residential and off-grid inverter products. These are not universal recommendations — actual appropriate sizing depends on your specific load calculation above.
| Inverter Size | Typical Use |
|---|---|
| 1 kW | Small loads / basic backup (lighting, electronics, small appliances) |
| 2 kW | Small home backup with a refrigerator, lighting, and entertainment devices |
| 3 kW | Medium household loads including computers, fans, and moderate appliance use |
| 5 kW | Larger household systems with multiple simultaneous appliances |
| 6 kW | Higher residential loads, including some motor-driven appliances |
| 8 kW | Large home or off-grid applications with substantial simultaneous demand |
| 10 kW+ | High-demand residential or small commercial applications |
Common Inverter Sizing Mistakes
Frequently Asked Questions
The right size depends on the combined running wattage of appliances you plan to power at once, plus extra surge power for motor-driven appliances during startup. Most homeowners add a 20–25% safety margin on top of that total. Use the calculator above with your own appliance list for a personalized estimate.
Add up running watts for simultaneous appliances, identify the largest surge/starting watts among them, take the higher of the running or surge-adjusted total, then apply a safety margin. Round the result up to a common inverter size such as 2 kW, 3 kW, or 5 kW.
Generally up to 5,000 watts of continuous output, with a separate, higher surge rating for a short duration. Continuous and surge ratings vary by manufacturer and model, so always check the specific datasheet.
It's actually more common for the DC solar array to be somewhat larger than the inverter's AC rating (a DC/AC ratio above 1.0), which can help output earlier and later in the day. Excessive oversizing can cause power clipping at peak sun hours.
Watts measure real power that performs work; VA (volt-amps) measures apparent power including reactive effects from motors. For resistive loads the two are similar; for motor-driven appliances, VA can run noticeably higher than watts.
Compressor startup commonly draws two to three times the running wattage briefly. A refrigerator running at roughly 150W may momentarily need 300–450W or more, depending on the model and age.
It depends on total simultaneous household load, the largest surge demand among your appliances, and your battery bank's discharge capability. Off-grid systems generally warrant more conservative sizing since there's no utility grid as backup.
A 10 kW array doesn't automatically require a 10 kW inverter — depending on the desired DC/AC ratio, many pair with somewhat lower AC-rated inverters. Final choice still depends primarily on your household's actual load and the manufacturer's input range.
Higher voltages like 48V are common in larger systems because they deliver more power at lower current, often reducing cable size and losses. Smaller systems with modest loads can still use 12V or 24V effectively — the right choice depends on total power needs.
Roughly 20–25% above your calculated maximum load is a common starting point, covering efficiency losses and everyday variability. Off-grid or safety-critical systems sometimes use a larger margin.
Many inverters can, but AC compressors have significant starting surge requirements, so the inverter needs to be sized for both running and surge wattage. Undersized inverters may fail to start the compressor or shut down under the surge load.
The inverter can only draw as much power as the battery bank can safely deliver. A battery with limited discharge current may cap real-world output even if the inverter is rated higher, and it affects how long a given load can be sustained.
Not sure about your solar array size yet?
Work out panel count and array capacity before finalizing your inverter choice.