Energy Consumption Calculator

Calculate battery runtime, appliance power consumption, and electricity costs.

🔋 Battery Runtime
📦 Battery Capacity Needed
💰 Electricity Cost

Calculate how long an appliance will run on a given battery.

Amp-hours
Nominal voltage
Watts consumed
Usable capacity limit
AC conversion loss

Calculate what battery capacity you need for a desired runtime.

Calculate the cost of running an appliance over time.

Check your utility bill

Common Appliance Power Draw

How to Calculate Battery Runtime

The fundamental formula for battery runtime is:

Runtime (h) = [Capacity (Ah) × Voltage (V) × DoD × Efficiency] / Power (W)

For example, a 100Ah 12V lead-acid battery (50% DoD) powering a 50W appliance through an 85% efficient inverter:

Runtime = [100 × 12 × 0.50 × 0.85] / 50 = 510 / 50 = 10.2 hours

The Depth of Discharge (DoD) is critical — lead-acid batteries should only be discharged to 50% to maximize lifespan, while LiFePO4 batteries can safely use 85-90% of their capacity. Always factor in inverter efficiency losses (typically 10-15%) when running AC appliances from a DC battery.

Battery Capacity Explained

Battery capacity is measured in two ways:

When comparing batteries of different voltages, always use Watt-hours for a fair comparison. A 100Ah 12V battery (1200Wh) stores the same energy as a 50Ah 24V battery (1200Wh).

Factors Affecting Real-World Runtime

FAQ

How accurate is this battery runtime calculator?
The calculator provides theoretical estimates based on ideal conditions. Real-world runtime is typically 10-30% lower due to temperature, battery age, Peukert's effect, and actual vs. rated capacity. Always add a 20% safety margin for critical applications.
What is Depth of Discharge (DoD) and why does it matter?
DoD is the percentage of battery capacity that has been used. Lead-acid batteries last longest when discharged only to 50%, while LiFePO4 batteries can safely use 85-90%. Discharging deeper reduces cycle life significantly — a lead-acid battery discharged to 80% may only last 300 cycles vs. 1000+ at 50% DoD.
Why do I need to account for inverter efficiency?
Inverters convert DC battery power to AC for household appliances, losing 10-25% of energy as heat in the process. If your load is purely DC (LED lights, phones via USB), select "DC load" for 100% efficiency.
How do I find my appliance's power consumption in watts?
Check the appliance label, manual, or use a plug-in wattmeter (kill-a-watt). For devices with motors or compressors (fridges, AC units), use the running wattage, not the higher startup surge wattage. The common appliances table above provides typical values.
How do I calculate how long a battery will last?
Use the formula: Runtime = (Battery Wh × Depth of Discharge × Efficiency) ÷ Load. Example: 12V 100Ah lithium battery (80% usable) = 960 Wh usable. At 85% inverter efficiency, that's 816 Wh. Powering a 50W device: 816 ÷ 50 ≈ 16.3 hours. Always factor in depth of discharge limits and conversion losses.
How much does it cost to run my appliance per month?
Multiply: (Watts × hours per day × 30 days) ÷ 1000 × your kWh rate. Example: A 200W TV running 4 hours/day at $0.15/kWh: (200 × 4 × 30) ÷ 1000 × 0.15 = $3.60/month. Use this calculator to compare appliances and identify energy hogs. Devices with heating elements (space heaters, dryers, water heaters) consume the most.
What's the difference between Ah and Wh?
Ah (amp-hours) measures charge capacity at a specific voltage. Wh (watt-hours) measures total energy regardless of voltage. Wh = Ah × Voltage. A 12V 100Ah battery and a 24V 50Ah battery both store 1200 Wh. Wh is more useful for comparing batteries of different voltages, while Ah is common in automotive specifications.
How do I size a battery for backup power?
List all essential loads and their wattage. Add them up, then multiply by the hours of backup needed. Add 20–30% safety margin for inefficiencies. For example: 500W total load × 8 hours = 4000 Wh + 25% margin = 5000 Wh (5 kWh). A 48V system would need about 104Ah of battery capacity. Consider lithium (LiFePO4) for longer cycle life and deeper discharge.

How to Use the Energy Consumption Calculator

  1. Enter your appliance's power rating in watts (W) — found on the device label, manual, or specification sheet.
  2. Set the daily usage hours — how many hours per day the appliance runs on average.
  3. Enter battery specifications (if applicable) — capacity in Ah or Wh and voltage to calculate runtime.
  4. Set your electricity rate — enter cost per kWh from your utility bill to estimate running costs.
  5. Review the results — daily/monthly/yearly energy consumption (Wh/kWh), estimated runtime on battery, and electricity costs.

Understanding Power Consumption and Battery Runtime

Electrical power consumption is measured in watts (W), representing the rate of energy use at any instant. Energy is power consumed over time, measured in watt-hours (Wh) — a 100W device running for 5 hours consumes 500 Wh (0.5 kWh). Your electricity bill charges by the kilowatt-hour (kWh), typically $0.10–0.35 per kWh in the US (€0.20–0.35 in Europe). To estimate any appliance's cost: (Power in W × hours per day × days per year) ÷ 1000 × cost per kWh. A 1500W space heater running 4 hours daily at $0.15/kWh costs about $329 per year.

Battery runtime calculation requires understanding the relationship between capacity, voltage, and power draw. Battery capacity is expressed in amp-hours (Ah) or watt-hours (Wh). A 12V 100Ah battery stores 1200 Wh of energy. To estimate runtime: Runtime (hours) = (Battery Wh × Depth of Discharge × Inverter Efficiency) ÷ Load (W). For a 12V 100Ah lead-acid battery (50% usable depth of discharge) powering a 100W load through an 85% efficient inverter: Runtime = (1200 × 0.50 × 0.85) ÷ 100 ≈ 5.1 hours. Lithium batteries allow 80–90% depth of discharge, significantly extending usable runtime.

Common appliance power ratings help you estimate usage without checking each device. LED bulbs: 5–15W. Laptop: 50–100W. Refrigerator: 100–400W (but runs intermittently, averaging 1–2 kWh/day). TV (LED, 55-inch): 60–100W. Air conditioner (window unit): 500–1500W. Microwave: 600–1200W. Electric water heater: 4000–5000W. When sizing a battery or solar system, add all critical loads and multiply by the hours of autonomy needed. Always include a safety margin of 20–30% for inefficiencies, surge currents, and battery aging.

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