Formula and worked example
Electricity cost = average watts ÷ 1,000 × hours × price per kWh.
At 120 W for 6 hours, consumption is 120 ÷ 1,000 × 6 = 0.72 kWh. At $0.20/kWh, the energy cost is $0.144, displayed as about $0.14.
Assumptions and limits
The example treats 120 W as the average draw for the whole six-hour attempt. A printer’s nameplate wattage is usually a maximum, so a plug-in meter or utility interval data can improve the input. Add a heated enclosure, filament dryer or other device separately when it runs for the job.