Wattage Calculator
Calculate watts, volts, amps, or ohms with Ohm's Law; build an appliance load profile; size a solar array or generator — free wattage calculator, no signup.
Wattage & Load Calculator
Add appliances from the preset library or enter custom loads. Get total wattage, daily kWh, monthly cost, and the solar system size needed to offset your usage.
| Appliance | Watts | Surge W | Hrs/Day | Qty | Wh/Day |
|---|
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What This Tool Covers
The Wattage Calculator totals the power draw and daily energy consumption of all your appliances. Add devices from a library of 50+ presets or enter custom values, and it returns total wattage, daily kWh, monthly kWh, annual kWh, peak demand, estimated monthly electricity cost, and the solar system size needed to offset your total usage.
Inputs Accepted
- • Appliance list: name, wattage, daily hours of use, quantity
- • Preset library with 50+ common appliances and typical wattages
- • Custom entries for any unlisted device
- • Local electricity rate ($/kWh) for cost calculation
Outputs Generated
- • Total connected wattage (W)
- • Daily energy consumption (kWh/day)
- • Monthly energy consumption (kWh/month)
- • Annual energy consumption (kWh/year)
- • Peak demand in watts (W)
- • Estimated monthly electricity cost ($)
- • Recommended solar system size to offset load
Features
50+ Appliance Preset Library
Select from a built-in list covering refrigerators, HVAC, water heaters, EVs, lighting, entertainment systems, and more. Each preset includes a typical wattage range you can adjust.
Solar System Size Output
Once you have your annual kWh total, the calculator translates it directly into a recommended solar system size using your state's peak sun hours - bridging load analysis and system sizing in one tool.
Monthly Cost Estimate
Enter your utility rate and get an immediate estimate of current monthly electricity cost - useful for comparing against a solar quote to validate claimed savings.
How It Works
Add Your Appliances
Select appliances from the preset library or add custom devices. For each item, confirm the wattage (adjust the preset if your device differs), enter daily hours of use, and set quantity.
Review Running Totals
As you add devices, the total wattage and daily kWh update in real time. You can see which appliances dominate your load - typically HVAC, water heating, and EV charging account for 60–70% of most homes.
Enter Your Electricity Rate
Add your current rate in $/kWh. The calculator multiplies annual kWh by this rate to estimate your current annual electricity spend - the baseline that solar savings are measured against.
Get Solar System Size Recommendation
The tool converts your annual kWh into a recommended solar system size (kW DC). Select your state to use the correct peak sun hours. This gives you a sizing estimate to compare against contractor proposals.
Use Cases
Off-Grid System Sizing
Off-grid designs start from a load analysis, not a utility bill. This tool builds that load list systematically, producing the daily kWh and peak demand figures needed to size batteries, inverters, and solar arrays.
Pre-Construction Load Estimation
New construction doesn't have a utility bill history. Use the appliance library to build a projected load list based on the planned appliances, then size a solar system accordingly before the building is complete.
Energy Efficiency Prioritization
See which appliances use the most energy. A 5,000W electric water heater running 2 hours a day uses 10 kWh - switching to a heat pump water heater (500W equivalent) saves 9 kWh/day, potentially more than adding 2 solar panels.
Calculation Methodology
Daily kWh per Appliance
Daily kWh = (Watts × Daily Hours × Quantity) ÷ 1000
Total Daily and Annual kWh
Annual kWh = ∑ Daily kWh (all appliances) × 365
Monthly Electricity Cost
Monthly Cost = (Annual kWh ÷ 12) × Rate ($/kWh)
Recommended Solar System Size
System kW = Annual kWh ÷ (PSH × 365 × 0.80 efficiency)
Pro Tips
Use nameplate wattage only as a ceiling. Most appliances don't run at their nameplate rating continuously. A 1,500W microwave runs for 5 minutes at a time. A 3,500W clothes dryer averages closer to 2,200W over a full cycle. Use actual running watts where possible, not maximum rated watts.
Include phantom loads. Electronics in standby mode still draw power - TVs, cable boxes, game consoles, and chargers together can add 100–200W of continuous low-level draw. Add a "standby loads" line item at 150W for 24 hours to capture this.
Cross-check against your utility bill. After building your appliance list, compare the total kWh/month to your actual utility bill. A large discrepancy (more than 20%) means you've missed a major load or overestimated hours for something. The two should roughly match.
Model future loads for correct solar sizing. If you're buying an EV next year, add it now. A 40 kWh/week EV charge adds about 170 kWh/month - enough to increase your system size by 1–2 kW. Size for what you'll actually use, not just what you use today.
Frequently Asked Questions
How do I find the wattage of my appliances?
Check the nameplate label on the device - usually on the back or bottom. It lists watts (W) or amps (A) and volts (V). If listed in amps, multiply amps by volts to get watts (e.g., 10A × 120V = 1,200W). For appliances with variable power (like HVAC), use average running watts, not peak startup watts.
What is the difference between peak demand and average demand?
Peak demand is the maximum simultaneous wattage if all listed appliances ran at once. Average demand is lower - most devices don't run simultaneously or continuously. For inverter and UPS sizing, use peak demand. For solar system sizing, use annual kWh (which reflects average demand over time).
Why does my appliance list total differ from my utility bill?
Several reasons: HVAC runtime varies by season and outdoor temperature; water heater usage varies by occupants; phantom loads are easy to miss; and some appliances have variable power draw. The wattage calculator gives a baseline - utility bills give the ground truth. Use both together.
Can I use this for a camper or RV?
Yes. Add your RV appliances (12V or 120V), enter daily hours of use, and the tool gives you daily kWh and recommended solar panel wattage for off-grid use. For 12V appliances, convert amps to watts using W = A × 12 before entering.
How many hours per day should I use for HVAC?
It depends on climate and system efficiency. In mild climates, a central AC system might run 4–6 hours per summer day. In hot climates it can run 8–12 hours. For annual average, 4–6 hours/day is a reasonable baseline for a 2,000 sq ft home in a mixed climate. Check your summer bills for a more accurate figure.
Does this calculator account for appliance efficiency ratings?
The presets use typical wattages for standard-efficiency appliances. If you have ENERGY STAR appliances, reduce the wattage accordingly. For example, a standard refrigerator uses about 150W average; an ENERGY STAR model may use 100W. Editing the preset wattage captures this difference.
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