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Home Energy Audit Calculator

Estimate your home's annual energy use, cost, intensity and HVAC share from its shell and major appliances.

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Appliance Energy Cost CalculatorTurn any appliance's wattage and daily use into a daily, monthly and yearly running cost in your currency.Capacitor energy calculatorCompute the energy stored in a capacitor from its capacitance and voltage (E = ½CV²).Inductor energy calculatorCompute the energy stored in an inductor from its inductance and current (E = ½LI²).E = mc² Calculator (Mass–Energy)Convert mass into energy and back with a realistic efficiency — 100 % for antimatter, 0.7 % for fusion, 0.09 % for fission — and read the result in joules, kWh, kcal and tonnes of TNT.Photon Energy CalculatorEnter a wavelength, a frequency or an energy and get all three from E = hf = hc/λ, in eV, keV, MeV and joules, with the spectral band named and the colour identified for visible light.Electricity price todayToday's and tomorrow's wholesale electricity prices per quarter hour for 16 European zones, with the cheapest hours, the daily average and negative prices.Heat Loss CalculatorAdd up the conductive heat loss through walls, windows, doors and roof from their area and R- or U-value.HVAC Sizing CalculatorEstimate the heating and cooling load of a room in BTU/hr, kW and tons from its area, climate and insulation.

Home Energy Audit Calculator is free to use as often as you like, directly from this page. Its place is under Energy & power; Appliance Energy Cost Calculator and Capacitor energy calculator answer the questions closest to this one.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What does Home Energy Audit Calculator do?

Estimate your home's annual energy use, cost, intensity and HVAC share from its shell and major appliances.

When would I actually use this?

Putting a number on a bill: what an appliance costs to run, whether a solar array covers the load, and how much heating a room actually needs.

What is the most common mistake?

Confusing power with energy. A kilowatt is a rate and a kilowatt-hour is a quantity; a 2 kW heater on for half an hour uses 1 kWh, and only the second figure appears on a bill.

How is Home Energy Audit Calculator different from Appliance Energy Cost Calculator?

They sit next to each other but answer different questions. Appliance Energy Cost Calculator: turn any appliance's wattage and daily use into a daily, monthly and yearly running cost in your currency. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Capacitor energy calculator is the closest one after this: Compute the energy stored in a capacitor from its capacitance and voltage (E = ½CV²).

What else is worth having open alongside it?

Inductor energy calculator and E = mc² Calculator (Mass–Energy) — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

The arithmetic is exact for the rating and the tariff you enter. Nameplate wattage is a maximum, not an average, and solar output depends on latitude, orientation and shading that no formula can guess.

Further reading

All guides →
ComparisonInsulate or Replace the Heating: Which Repays First, and Why the Answer InvertsPut both on one axis — euros paid per kilowatt-hour a year of permanent saving — and the comparison becomes decidable. The same loft job costs 0.83 euros per kilowatt-hour a year in a 1965 house and 5.00 in a 2005 one, a factor of six. That, and not the age of the building by itself, is what inverts the verdict.How-toHow to Estimate the Running Costs of a HomeAdd up energy, water, heating, and maintenance with simple rules of thumb so you know what a home really costs to run each month.ComparisonHeat Pump or Gas Boiler: the SCOP Your Local Prices DemandBefore any grant, the price of electricity divided by the price of gas sets a seasonal efficiency the heat pump must beat just to break even on running cost. In late 2025 that number was 1.53 in Portugal and 2.79 in Germany — and on old radiators a German heat pump can cost more to run than the boiler it replaced.ExplainerCapacitors in Series: the Smallest One Decides, and Then It Fails100, 220 and 330 µF in series come to 56.9 µF — less than the smallest. Put 100 µF and 1 µF in series and the total is 0.99 µF, while the small one carries 99 % of the voltage.ExplainerOne Time Constant Is 63 % of the Way, Not the End1,000 Ω with 100 µF gives a time constant of 0.1 s. The capacitor is 63 % charged at that point, 95 % after three constants and 99.3 % after five — the last of which is the number that matters.ExplainerA 5,000 mAh Power Bank Does Not Hold 5,000 mAh for Your Phone5,000 mAh drawn at 500 mA with 85 % efficiency runs for 8.5 hours instead of the arithmetic's 10. The same 15 % explains why a 5,000 mAh bank barely fills a 4,000 mAh phone once.