Window AC cost formula?
kWh/day = (W_eff ÷ 1,000) × hours; cost = kWh × $/kWh. W_eff can be nameplate watts or BTU÷EER, times duty cycle.
A window AC cost calculator answers how much electricity a window air conditioner may cost to run under the usage you enter.
Start with nameplate or measured watts when you have them — that is the most direct electrical input. If the label lists cooling BTU/hr and EER, switch to BTU + EER mode: EER can be used with cooling capacity to estimate rated electrical input (watts ≈ BTU/hr ÷ EER). BTU is cooling capacity, not watts.
CEER is a combined room-air-conditioner efficiency metric that also accounts for standby/off-mode consumption and should not be substituted directly for EER in this running-watt calculation.
Energy per day (kWh) = effective watts ÷ 1,000 × hours/day. Cost per day = energy × your electricity rate. Multiply by the usage days you choose for a month or season total. Optional average runtime (duty cycle) scales nameplate draw when you assume the compressor is not at full load for every operating hour.
Results are estimates for planning. Real bills also depend on outdoor temperature, thermostat settings, insulation, cycling, and how your utility bills energy.
Concise answers for common searches — definitions, steps, and comparisons.
kWh/day = (W_eff ÷ 1,000) × hours; cost = kWh × $/kWh. W_eff can be nameplate watts or BTU÷EER, times duty cycle.
At 8 hours and $0.15/kWh with 100% average runtime: about 4 kWh and $0.60/day.
Convert watts to kilowatts, multiply by hours and days, then apply your rate. Duty cycle optionally scales average watts. BTU mode estimates rated input as BTU ÷ EER.
Formula
watts_full = nameplate watts, or BTU ÷ EER; watts_eff = watts_full × (dutyCyclePct ÷ 100); kWh/day = (watts_eff ÷ 1,000) × hoursPerDay; cost/day = kWh/day × pricePerKwh; period cost = cost/day × days. Week = ×7; 30-day view = ×30; 365-day view = ×365 (same daily use, labeled as extrapolation).Prefer nameplate or measured watts. If you only have cooling BTU/hr and EER, use BTU + EER mode so rated input is estimated as BTU ÷ EER. Do not enter CEER as EER.
Hours are operating time. Set days to 30 for a month-style check, 90 for a summer season, or another period you care about.
Use $/kWh or ¢/kWh from your utility bill. Replace the example default rate.
Leave at 100% for a full-load ceiling on the hours entered. Try 75% or 50% if you assume substantial compressor cycling.
The primary result is estimated cost per day. Secondary rows show energy, week, 30-day, your period, and a labeled 365-day extrapolation.
Input
watts 500 · hours 8 · days 30 · rate $0.15/kWh · duty 100%Output
4 kWh/day · $0.60/day · 120 kWh / $18 over 30 days(500 ÷ 1000) × 8 = 4 kWh/day. 4 × 0.15 = $0.60/day. Over 30 days: 120 kWh and $18.
Input
watts 500 · hours 4 · rate $0.15 · duty 100%Output
2 kWh/day · $0.30/day(0.5) × 4 = 2 kWh; 2 × 0.15 = $0.30.
Input
watts 500 · hours 8 · rate $0.15 · duty 75%Output
3 kWh/day · $0.45/dayEffective watts = 375; (0.375) × 8 = 3 kWh; 3 × 0.15 = $0.45.
Input
btu 5000 · eer 10 · hours 8 · days 30 · rate $0.15Output
~500 W · 4 kWh/day · $0.60/day · $18 / 30 daysWatts ≈ 5000 ÷ 10 = 500, then the same path as the watts worked example.
Common real-world scenarios where this tool saves time.
500 W · 8 hr/day · $0.15/kWh → about 4 kWh/day and $0.60/day.
Same daily use for 30 days → about 120 kWh and $18 at $0.15/kWh.
5,000 BTU ÷ 10 EER → ~500 W full-load estimate, then apply hours and rate.
Set usage days to 90 (or your season length) so the period cost matches how long you actually run the unit.
Step-by-step chains that connect related tools for common tasks.
Estimate room cooling load, then project window AC electricity cost.
| Power | Hours/day | kWh/day | Approx. $/day |
|---|---|---|---|
| 500 W | 8 | 4 | $0.60 |
| 500 W | 4 | 2 | $0.30 |
| 1000 W | 5 | 5 | $1.00 |
| 800 W (ex. 8k BTU ÷ 10 EER) | 8 | 6.4 | $0.96 |
A kill-a-watt meter or the electrical rating on the label beats guessing. Use BTU ÷ EER only when watts are unavailable.
A 30-day check and a 90-day season answer different questions. Set usage days explicitly.
Compare 100% vs 75% average runtime to see how cycling assumptions change cost — without treating either as a measurement of your compressor.
BTU/hr is cooling capacity. Electrical watts come from the nameplate, a meter, or BTU ÷ EER in efficiency mode.
CEER includes standby/off-mode consumption. Use EER for BTU ÷ EER rated-input estimates, or prefer nameplate watts.
15 ¢/kWh is $0.15/kWh. Use the ¢/kWh toggle, or convert cents ÷ 100 before entering dollars.
Rated watts are a full-load planning figure. Compressors cycle. Use measured average watts or a lower average-runtime % if you want a softer estimate.
Enter hours per day, then set usage days. Do not put monthly hours into the hours/day field.
Replace the example $/kWh with the energy charge from your utility statement.
Period cost uses the days you entered. The 365-day row is a same-daily-use extrapolation and is labeled that way.
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Daily cost ≈ (watts ÷ 1,000) × hours/day × $/kWh, optionally scaled by average runtime %. Example: 500 W × 8 hr × $0.15/kWh ≈ $0.60/day at 100% runtime.
Multiply daily energy by your usage days and rate. At 500 W, 8 hr/day, 30 days, and $0.15/kWh, that is about 120 kWh and $18. Change days if your month of use is shorter.
Energy in kWh = (effective watts ÷ 1,000) × hours. A 500 W unit for 8 hours uses about 4 kWh that day at 100% average runtime.
BTU alone is not watts. If EER is about 10, watts ≈ 5000 ÷ 10 = 500 W. At 8 hr/day and $0.15/kWh that is roughly $0.60/day — an estimate until you confirm nameplate watts and your rate.
With EER 10, watts ≈ 8000 ÷ 10 = 800 W. At 8 hr/day and $0.15/kWh that is about 6.4 kWh/day and roughly $0.96/day at 100% average runtime. Prefer the label’s watts when available.
Relative to a lamp, yes — hundreds to over a thousand watts while cooling. Relative to whole-home central AC, a single window unit is usually smaller. Hours per day and your $/kWh dominate the bill impact.
Not directly. BTU/hr is cooling capacity. Electricity cost follows watts (or BTU ÷ EER), hours, and rate.
No. EER can be used with cooling capacity to estimate rated electrical input. CEER is a combined room-air-conditioner efficiency metric that also accounts for standby/off-mode consumption and should not be substituted directly for EER in this running-watt calculation. Prefer nameplate watts when available.
Use the energy charge from your utility bill in $/kWh (or ¢/kWh). The calculator’s default is an example only — not a universal U.S. price.
It is the percent of entered operating hours you assume the unit draws its full entered (or BTU-derived) watts. 100% is a full-load ceiling on those hours; 75% means three-quarters of that average draw. It is a planning assumption, not a measurement of your compressor.
Window AC cost inputs stay in your browser — EverydayTools does not collect window-ac-cost calculator entries.
Estimates only — not a utility bill, energy audit, or HVAC sizing guarantee. Actual consumption varies with cycling, rates, and conditions.
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Reviewed on 2026-09-10.
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Examples only — replace with your watts, hours, and rate.
Prefer nameplate watts when available. BTU mode estimates rated electrical input as BTU/hr ÷ EER — not CEER.
Watt chips are example estimates — use your nameplate when you can.
Nameplate or measured running watts
Hours the unit is operating (plugged on / cooling available)
e.g. 30 for a month check, 90 for a summer season — period cost uses this field
Example default is not a universal US price — use your bill
100% = full entered watts for all operating hours. 75% = three-quarters of that average draw.
This is a planning assumption for compressor cycling — not a measurement of your specific unit.