Watts, Kilowatt-Hours, and Why Your Bill Is What It Is

Some calculations matter for a single decision; this one matters for years. Your bill is in kWh. Your appliances are rated in watts. Multiplying by hours gives the answer.

The formula

kWh = (watts × hours) / 1000. A 1500W heater running 4 h/day = 6 kWh/day.

What costs most

Resistive heating (heaters, dryers, ovens) and air conditioning dominate most bills.

Standby (vampire) draw

TVs, consoles, chargers — 0.5–5W each, but 24/7. Can be 8–10% of total bill.

Pro tips

• A smart plug with energy monitoring identifies hidden draws in a weekend.
• LEDs use 80% less energy than incandescents — payback in months, not years.

Frequently asked questions

How much does charging a phone cost? Less than $1/year. Not worth optimising.

Does shutting down beat sleep mode? Marginally. Sleep draws 1–3 W; shutdown <1 W. Worth it for desktops, not laptops.

Run your own numbers before you trust a rule of thumb. Two minutes saves a lot of regret.