Electricity Calculator
Estimate monthly and annual electricity cost for an appliance from its wattage, daily usage hours, and electricity rate per kWh.
How It's Calculated
Formula
\text{dailyKWh} = \frac{\text{watts}}{1000} \times \text{hoursPerDay} \\ \text{monthlyCost} = \text{dailyKWh} \times 30 \times \text{rate} \\ \text{annualCost} = \text{dailyKWh} \times 365 \times \text{rate}This calculator estimates what a single appliance costs to run by converting its wattage and daily usage into energy consumed, then multiplying by your electricity rate. First, daily energy use in kilowatt-hours (kWh) is found by dividing wattage by 1000 (to convert watts to kilowatts) and multiplying by hours used per day. Monthly and annual energy use scale that daily figure by an explicit 30-day month and 365-day year — not a fractional average like 30.4375 days/month, and not a 12x30 shortcut for the annual figure, so the two periods use consistent, easy-to-verify multipliers. Cost is simply energy used multiplied by your entered electricity rate per kWh; this calculator does not apply tariff tiers, standing charges, taxes, or peak/off-peak pricing — it assumes a single flat rate you provide yourself.
Worked Examples
1000 W appliance, 2 hours/day, rate 0.15/kWh
- Daily energy = 1000 / 1000 x 2 = 2 kWh
- Monthly energy = 2 x 30 = 60 kWh; Monthly cost = 60 x 0.15 = 9.00
- Annual energy = 2 x 365 = 730 kWh; Annual cost = 730 x 0.15 = 109.50
Zero usage
- Daily energy = 1000 / 1000 x 0 = 0 kWh
- Monthly cost = 0 x 30 x 0.15 = 0.00 — zero hours per day means zero cost.
Frequently Asked Questions
Why 30 days for the month and 365 days for the year instead of a more precise average?
This calculator uses an explicit, easy-to-verify calendar convention — 30 days per month and 365 days per year — rather than a fractional average like 30.4375 days/month or deriving the annual figure as 12 x 30 days. That keeps the monthly and annual figures independently checkable against the same daily energy number.
Does this account for tariff tiers, standing charges, or taxes?
No. This calculator applies a single flat rate per kWh that you provide. It does not model tiered/block tariffs, fixed standing charges, taxes, or time-of-use (peak/off-peak) pricing — if your utility bill includes any of those, treat this as an estimate of the usage-based portion only.
Can hours per day be more than 24?
No. Hours used per day must be between 0 and 24, since a single day cannot have more than 24 hours of appliance runtime.
Is zero usage a valid input?
Yes. Zero wattage, zero hours per day, or a zero electricity rate are all valid and simply produce a zero cost result — this calculator is pure multiplication, so there's no division-by-zero concern.