50 watts to kWh per day and month

1.20 kWh/day

for 50 W running 24/7 · 36 kWh/month · $5.94/month at 16.5¢

50 W by hours of use

Use	Per day	Per month	Cost/month
1 h/day	0.05 kWh	1.5 kWh	$0.25
2 h/day	0.10 kWh	3.0 kWh	$0.49
4 h/day	0.20 kWh	6.0 kWh	$0.99
8 h/day	0.40 kWh	12.0 kWh	$1.98
12 h/day	0.60 kWh	18.0 kWh	$2.97
24 h/day	1.20 kWh	36.0 kWh	$5.94

kWh = W × hours ÷ 1000. Devices with thermostats or compressors cycle, so actual use is often lower than the rated wattage × hours.

1.20 kWh running 24 hours, 0.40 kWh at 8 hours.