If you have ever looked at your power bill and wondered "which appliance is driving this?", this guide gives you a clean way to estimate cost per day or month.
For full system planning, use the WattSizing Calculator.
Quick Answer
Use:
Cost = (Watts x Hours / 1000) x Electricity Rate
Where rate is in $/kWh.
Example: 1,500 W heater x 3 h/day at $0.20/kWh:
(1500 x 3 / 1000) x 0.20 = $0.90/day
Full Calculation Method
- Find appliance watts (label, manual, or plug-in meter).
- Estimate average hours used per day.
- Convert to daily kWh.
- Multiply by your local utility rate.
- Multiply by 30 for a monthly estimate.
Need a refresher on step 3? See How to Calculate kWh from Watts and Hours.
Appliance Cost Table (at $0.18/kWh)
| Appliance | Typical Watts | Daily Use | Daily Cost | Monthly Cost (30 days) |
|---|---|---|---|---|
| LED TV | 120 W | 5 h | $0.11 | $3.24 |
| Laptop | 65 W | 8 h | $0.09 | $2.81 |
| Microwave | 1,300 W | 0.4 h | $0.09 | $2.81 |
| Space heater | 1,500 W | 4 h | $1.08 | $32.40 |
| Dehumidifier | 500 W | 10 h | $0.90 | $27.00 |
Worked Example: Refrigerator
Suppose your fridge averages 150 W over a full day (after cycling).
- Daily kWh:
(150 x 24) / 1000 = 3.6 kWh - Daily cost at $0.16/kWh:
3.6 x 0.16 = $0.58 - Monthly cost (30 days):
$0.58 x 30 = $17.28
For fridges, average measured watts are more reliable than compressor nameplate watts. For details, read How Many Watts Does a Refrigerator Use.
Practical Accuracy Tips
- Include duty cycle (not all appliances run at full power continuously).
- Use a plug meter for electronics and kitchen devices.
- For seasonal loads (AC/heating), estimate by season, not yearly average.
- Check tiered or time-of-use rates if your bill structure is complex.
FAQs
Is cost estimated from rated watts always accurate?
Not always. Nameplate watts can overestimate or underestimate real usage depending on cycling behavior and operating mode.
Which matters more: watts or hours?
Both. A low-watt device run all day can cost more than a high-watt device used briefly.
Can I estimate cost without my exact electricity rate?
Yes. Use a national/local average first, then update with your real bill rate for better accuracy.
Should I include standby power?
Yes for full-home estimates. Many devices draw small but continuous standby loads that add up monthly.
CTA
Want your total appliance bill impact in one place? Use the WattSizing Calculator to model daily kWh and running cost across your whole load list.
