Electricity cost is just a 3-step conversion

Most people see “watts” on a label and can’t translate it into money. This calculator bridges that gap. Under the hood, it uses the same math your utility company uses for the energy portion of your bill: convert power (watts) into energy (kilowatt-hours), then multiply by your electricity rate.

Here’s the key idea: watts are speed (how fast electricity is being used), while kilowatt-hours (kWh) are distance (how much electricity you actually used over time). Your bill charges you for “distance”, not “speed”.

1,000 watts = 1 kilowatt. So we convert: kW = watts ÷ 1000. A 1500W space heater is 1.5 kW. A 9W LED bulb is 0.009 kW.

Energy is power multiplied by time: kWh = kW × hours. If something is 1.5 kW and runs for 2 hours, it uses 3 kWh. If it runs for 2 hours/day for 30 days, that’s 60 kWh in a month.

Cost is: Cost = kWh × rate. If your rate is $0.16 per kWh, then 60 kWh costs $9.60 (energy charge portion).

• Multiple devices: if you have 6 bulbs or 2 monitors, cost scales correctly.
• Standby power: accounts for “always plugged in” energy drain.
• Time horizons: shows hour/day/month/year so you can plan and prioritize upgrades.
• Optional CO₂: lets you estimate impact if you know a factor for your grid.

The exact formulas used

• Active kW: kW = (watts × devices) ÷ 1000
• Active kWh/day: kWh/day = kW × hours/day
• Active kWh/month: kWh/month = kWh/day × days/month
• Active cost/month: $/month = kWh/month × rate

If you enter standby watts and standby hours/day, the calculator estimates standby energy separately and adds it:

• Standby kW: kW = (standbyWatts × devices) ÷ 1000
• Standby kWh/month: kWh/month = standby kW × standby hours/day × days/month
• Total kWh/month: active + standby
• Total cost/month: total kWh/month × rate

If you enter a CO₂ factor in kg per kWh, then: CO₂/month (kg) = total kWh/month × CO₂ factor. Leave it blank if you don’t want this.

The meter is a quick visual based on monthly cost. It’s not “good or bad” — it’s meant to help you spot which devices dominate your bill.

Real-world examples you can copy

You run a 1500W space heater for 4 hours/day, 30 days/month, at $0.18/kWh.

• kW = 1500 ÷ 1000 = 1.5 kW
• kWh/day = 1.5 × 4 = 6 kWh/day
• kWh/month = 6 × 30 = 180 kWh/month
• Cost/month = 180 × 0.18 = $32.40/month

This is why “small heaters” can quietly add a noticeable chunk to bills — they’re high wattage for long hours.

Six 9W LED bulbs used 5 hours/day, 30 days/month, at $0.18/kWh:

• Total watts = 9 × 6 = 54W → 0.054 kW
• kWh/day = 0.054 × 5 = 0.27 kWh/day
• kWh/month = 0.27 × 30 = 8.1 kWh/month
• Cost/month = 8.1 × 0.18 = $1.46/month

That’s why LED lighting is usually not the “big bill villain” — heating/cooling and large motors are.

Your TV uses 120W for 3 hours/day, but also 3W standby for 21 hours/day. At $0.20/kWh:

• Active: 0.12 kW × 3 h/day × 30 = 10.8 kWh/month → $2.16/month
• Standby: 0.003 kW × 21 h/day × 30 = 1.89 kWh/month → $0.38/month

Standby is usually small per device — but across many devices (TV, console, speakers, chargers), it adds up.

• Save each scenario and compare your top 3 “power hogs”.
• Try reducing hours/day (behavior change) vs reducing watts (new device).
• Share the result as “$X/month” — it lands instantly in social posts.

Frequently Asked Questions

• Is this the same as my total electricity bill?

  Not always. This estimates the energy charge for a device (kWh × rate). Your bill may include fixed fees, delivery charges, taxes, tiered pricing, time-of-use rates, and demand charges. Use this tool to compare devices and behaviors, not to predict a bill down to the cent.

• My appliance has amps (A) and volts (V), not watts. What do I do?

  You can estimate watts with Watts = Volts × Amps (for many devices). Example: 120V × 2A ≈ 240W. If you can, use the watt rating printed on the label for best accuracy.

• Why does my fridge wattage not match real usage?

  Fridges cycle on and off. The “watts” label may reflect running power, not average power. For cycling devices, use an average wattage (or fewer hours/day) to reflect typical operation.

• What’s a normal electricity rate?

  Rates vary by region and plan. Many people see something like $0.12–$0.35 per kWh. Your bill is the truth source — copy the $/kWh you actually pay for the most accurate estimates.

• How do I use this to reduce my bill fast?

  Focus on high-wattage + high-hours devices first: space heaters, AC, dryers, ovens, and EV charging. Small electronics matter less unless you have lots of them running many hours.

• Does the CO₂ estimate mean “bad”?

  No — it’s informational. If you enter a factor, it translates kWh into an approximate kg CO₂ number. Different grids and energy mixes vary a lot, so treat it as a directional estimate.