How much energy do my home appliances actually use, and what does it cost?

The one formula behind every appliance calculator here

Energy is power × time. Take the watts on the label, multiply by the hours the appliance actually runs in a day, and divide by 1,000 to get kilowatt-hours (kWh) — the unit your bill charges for. Cost is then kWh × your rate. Every calculator in the home-energy category is this formula with the awkward parts filled in for you: duty cycles, standby draw, and the presets for real appliances.

The awkward part that matters most is “actually runs.” A fridge's compressor cycles, a heater's thermostat clicks off, and a microwave's 1,000 W lasts minutes. Nameplate watts alone tell you almost nothing about the bill.

A worked day, using the site's own appliance list

The tiny house solar calculator ships a “Modern Tiny Home” preset with four appliances and their hours. It is a clean test of the formula, because the loads are small enough to check by hand:

• That is about 128 kWh a month. At $0.17/kWh — the rate used in the site's refrigerator calculator presets — it costs roughly $21.83 a month.
• The fridge is 56% of the day's energy on 100 W. The microwave is 12% of it on 1,000 W. If you only remember one line from this guide, make it that one.

Where the real money hides: always-on and always-hot

Scale the same thinking up to a full house and two patterns repeat. First, age matters more than size for 24-hour appliances — and the refrigerator calculator does not stop at the label rating: it multiplies it by age, seal, temperature, and ice-maker factors. Run its presets and a recent ENERGY STAR fridge rated 450 kWh a year comes out at 569 kWh ($96.77 at $0.17/kWh) once its 3–5-year age factor (×1.1) and French-door ice maker (×1.15) are applied, while the 20-year-old preset rated 1,200 kWh lands at 2,640 kWh ($448.80) under a ×2 age factor and ×1.1 for fair seals. That is a $352.03 yearly difference from one appliance you never switch off.

Second, resistive heat is the one load that is both big and long-running. A 1,500 W space heater — the example load in the extension cord calculator — used 8 hours a day consumes 12 kWh daily, nearly three times the whole tiny-home day above, and about $61.20 a month at the same $0.17 rate. Water heating, pool pumps, and dehumidifiers live in the same category, which is why each has its own calculator in the hub: their hours, not their labels, decide what they cost you.

A quick way to audit your own house

You do not need a meter on every socket. Three passes find most of the bill:

• List everything that runs 24 hours (fridge, freezer, network gear, standby loads) and multiply watts × 24. This is your floor — it never sleeps.
• Add the heat-and-water loads with honest hours: water heater, space heaters, pool pump, dehumidifier.
• Only then add the occasional big loads — oven, microwave, washer, tools — with their real minutes per day. They usually shrink to a rounding error next to the first two lists.