How we calculate

Every number on this site comes from a public source or a formula written out below.

Electricity prices, usage and bills

Source: U.S. Energy Information Administration (EIA), electricity retail sales, residential sector, by state and month (API route electricity/retail-sales). EIA collects these figures from utilities and publishes them in its Electric Power Monthly, usually about two months after the month ends. This site checks for new data every week and rebuilds when EIA publishes a new month.

• Price (cents per kWh) is EIA's average price: total residential revenue divided by kWh sold. It therefore includes delivery charges and fees that utilities bill per kWh.
• Average monthly usage = residential kWh sold ÷ number of residential customers, averaged over the latest 12 months.
• Average monthly bill = residential revenue ÷ number of residential customers, averaged over the same 12 months. It includes fixed charges collected through rates; local taxes may be excluded.
• Change is the price compared with the same month a year earlier.

Monthly figures are preliminary and EIA revises them; when it does, the site picks up the revision on the next weekly check.

Solar output

Source: PVWatts v8 by the National Laboratory of the Rockies (formerly NREL), for one large city per state, using a fixed roof-mounted system facing south (180° azimuth) at a 20° tilt with 14% system losses and standard modules. Your roof's direction, shading and tilt change the result.

Calculators

Each calculator page explains its own formula. The math runs in your browser; nothing you type is sent anywhere.

What these numbers are not

They are averages and estimates for planning. They are not a quote, a bill, or financial, tax or legal advice. Your utility's tariff and your installer's or contractor's quote are the final word.