Inverter Load Calculator
An inverter load calculator helps you determine the right inverter capacity and battery backup time by working through your home's actual appliance wattage, rather than guessing or over-buying "to be safe." This guide functions as a manual calculator: use the appliance wattage reference tables below, follow the calculation steps, and you'll arrive at the exact VA rating and backup duration you need, the same output a paid online calculator tool would give you, just done transparently so you understand every number.
If you want the underlying formula explained in more depth with worked examples, our companion guide on how to calculate load for inverter walks through the step-by-step method. This page focuses on giving you the reference data and quick-lookup tables to run the calculation yourself right now.
Inverter load calculator: appliance wattage reference table
Appliance | Running watts | Startup surge (if motor-driven) |
LED bulb (single) | 7 to 15W | None |
CFL bulb | 15 to 25W | None |
Tube light (LED) | 18 to 22W | None |
Ceiling fan | 60 to 80W | Minimal |
Table/pedestal fan | 50 to 75W | Minimal |
LED TV (32 inch) | 60 to 80W | None |
LED TV (42-50 inch) | 100 to 150W | None |
Laptop | 40 to 65W | None |
Desktop computer | 150 to 300W | None |
Wi-Fi router | 10 to 15W | None |
Refrigerator (direct cool, 180L) | 100 to 150W | 3 to 4x running |
Refrigerator (frost-free, 250L+) | 150 to 250W | 3 to 5x running |
Water pump (0.5 HP) | 370W | 2 to 3x running |
Water pump (1 HP) | 750W | 2 to 3x running |
Mixer grinder | 400 to 750W | 1.5 to 2x running |
Washing machine (top-load) | 400 to 800W | 1.5 to 2x running |
Microwave oven | 1,000 to 1,500W | None (resistive load) |
Iron (electric) | 750 to 1,200W | None (resistive load) |
Air conditioner (1 ton, inverter type) | 900 to 1,200W | 2 to 3x running |
Air conditioner (1.5 ton) | 1,500 to 1,800W | 2 to 3x running |
Step 1: Build your appliance list
Using the table above, list only the appliances you'll run simultaneously during a power cut. Most homes prioritise: lights, fans, TV, refrigerator, and Wi-Fi router as the "essential backup" list, since air conditioners and heavy motors are usually excluded from standard home inverter setups (they typically need generators or dedicated high-capacity systems).
Step 2: Calculate using this quick reference
Household size | Typical essential appliance list | Approximate running load | Recommended inverter (with margin) |
Small (1-2 rooms) | 4 LED bulbs, 2 fans, 1 TV | 250 to 350W | 700 to 850 VA (Round to 1 kVA) |
Medium (2-3 rooms) | 6-8 LED bulbs, 3 fans, 1 TV, 1 fridge | 500 to 650W | 1,300 to 1,600 VA (1.5 kVA) |
Large (3-4 rooms) | 10+ bulbs, 4-5 fans, 1-2 TVs, 1 fridge, 1 water pump | 1,000 to 1,300W | 2,500 to 3,200 VA (3 kVA) |
Large with AC backup | All of the above + 1 AC unit | 2,200 to 2,800W | 5,000+ VA (5 kVA, requires dedicated setup) |
This table gives you an instant starting point. For an exact calculation specific to your appliance list, follow the detailed formula walkthrough in our how to calculate load for inverter guide.
Backup time calculator: how long will your battery last?
Once you know your load (from the calculator above), use this formula to estimate backup duration:
Backup Time (hours) = (Battery Capacity in Ah x Battery Voltage x Depth of Discharge x Inverter Efficiency) ÷ Total Load in Watts
Worked example
A 150 Ah, 12V battery, with 50% depth of discharge (standard recommendation for VRLA/tubular batteries) and 85% inverter efficiency, running a 600W load:
Backup Time = (150 x 12 x 0.5 x 0.85) ÷ 600 = 765 ÷ 600 = 1.275 hours (approximately 1 hour 16 minutes)
Backup time reference table (for common battery sizes at 500W load)
Battery capacity | Backup time at 500W load (approx) |
100 Ah, 12V | 1 hour |
150 Ah, 12V | 1.5 hours |
200 Ah, 12V | 2 hours |
2 x 150 Ah, 12V (parallel) | 3 hours |
These figures assume 50% depth of discharge and 85% inverter efficiency, standard assumptions for VRLA and tubular batteries used in Indian home inverter systems.
How to use this calculator for battery selection
Your priority | What to check |
Longest possible backup | Higher Ah battery, or multiple batteries in parallel |
Lowest cost | Match battery Ah closely to your actual load needs without excessive oversizing |
Frequent long power cuts | Consider tubular batteries (handle deeper discharge better than VRLA) |
Minimal maintenance | VRLA/SMF batteries, even if slightly shorter lifespan than tubular |
For more on choosing between VRLA and tubular battery types for your inverter, see our detailed VRLA battery guide.
Common inverter load calculator mistakes to avoid
- Including appliances you won't run together. Calculate for realistic simultaneous usage, not every appliance in your house
- Ignoring motor startup surge. Fridges and pumps need extra capacity beyond their running wattage to start
- Using 100% depth of discharge in battery calculations. This shortens battery life dramatically; 50% is the safe standard for VRLA batteries
- Not leaving room for future appliances. If you plan to add an AC or additional fridge, size your inverter with some headroom now
FAQs
What is an inverter load calculator?
An inverter load calculator is a tool or method that helps you determine the correct inverter VA capacity and expected battery backup time based on your home's appliance wattage. It prevents both undersizing (unreliable power) and oversizing (wasted money).
How accurate is a manual inverter load calculator versus an online tool?
Equally accurate, since both use the same underlying formula: total running watts plus startup surge, adjusted by a safety margin, divided by power factor. An online tool simply automates the same calculation this guide walks you through manually.
What is the average inverter load for an Indian home?
For a medium home (2-3 rooms) running lights, fans, TV, and a refrigerator, average running load is 500 to 650W, translating to a recommended 1.5 kVA inverter after applying safety margin and power factor adjustment.
How do I calculate battery backup time using an inverter load calculator?
Use the formula: Backup Time (hours) = (Battery Ah x Voltage x Depth of Discharge x Inverter Efficiency) ÷ Total Load in Watts. For a 150 Ah, 12V battery at 50% DoD and 85% efficiency running a 500W load, backup time is approximately 1.5 hours.
Should I include my air conditioner in the inverter load calculator?
Generally no for standard home inverters, since AC units require very high capacity (1,500W+ running, higher surge) that typically needs a dedicated high-capacity inverter (5 kVA+) or a separate backup solution rather than sharing your standard home inverter circuit.
What depth of discharge should I use in my calculation?
50% is the standard safe assumption for VRLA and tubular batteries. Using 100% depth of discharge in your calculation will show a longer backup time on paper, but repeatedly discharging batteries that deeply significantly shortens their real lifespan.
Can I use this calculator for solar inverter systems too?
The load calculation principles (total watts, surge, safety margin, power factor) apply the same way to solar inverters. However, solar systems also need calculations for panel capacity and daily sun-hours, which are separate additional factors beyond just load calculation.
What happens if I undersize my inverter based on incorrect load calculation?
An undersized inverter will trip, shut down, or fail to start motor-driven appliances like fridges and pumps when their startup surge exceeds the inverter's capacity. This leads to repeated failures during exactly the power cuts you bought the inverter to handle.
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