Air Conditioner Electricity Cost
Calculate your air conditioner monthly electricity cost from BTU rating, SEER or EER efficiency, daily runtime hours, and your electricity rate.
Air conditioners are often the single largest contributor to summer electricity bills. A 3-ton central AC (36,000 BTU) with a SEER rating of 14 running 8 hours a day costs roughly $100-130 per month at average U.S. rates.
SEER vs EER
SEER (Seasonal Energy Efficiency Ratio) is the standard rating for central air conditioners and measures efficiency over a full cooling season. EER (Energy Efficiency Ratio) is used for window units and measures efficiency at a fixed test condition (95 F outside, 80 F inside, 50% humidity).
For this calculator, enter the SEER or EER value from the unit nameplate or specifications. The math is the same either way.
The formula
Watts = BTU_per_hour / EER (or SEER)
kWh per day = Watts / 1,000 x runtime_hours
Monthly cost = kWh per day x 30 x electricity_rate
Interpreting BTU ratings
AC capacity is rated in BTU/hour. Common sizes: 5,000 BTU (small window unit, ~150 sq ft), 12,000 BTU (1 ton, ~550 sq ft), 24,000 BTU (2 ton, ~1,000 sq ft), 36,000 BTU (3 ton, ~1,500 sq ft). Larger is not always better — an oversized unit short-cycles, runs inefficiently, and removes less humidity.
Minimum SEER ratings have risen over the years. Units sold today must be at least SEER 14 in northern states and SEER 15 in southern states. High-efficiency units reach SEER 20-25. The jump from SEER 14 to SEER 18 cuts electricity use by roughly 22%.
Runtime estimate
A well-sized AC in a typical climate runs 8-12 hours on a hot summer day. On peak days, runtime can reach 16-20 hours. For annual cost, sum the monthly usage across the cooling season rather than multiplying 12 months of peak-day runtime.