AC Electricity Cost Calculator: Units per Hour and Bill

A 1 ton DC inverter AC uses about 0.7 units an hour on a hot day at 26°C, a 1.5 ton inverter about 1 unit and a 2 ton inverter about 1.4. Non-inverter ACs of the same size use roughly 1.2, 1.8 and 2.4 units an hour while the compressor runs.

The calculator turns that into units for the month and prices them the way your bill does. It adds the AC's units to what your home already uses, because the slab rate is set by your total units. So the cost shown is the real extra on your bill, not a flat rate per unit.

AC units per hour, day and month

Typical use at 26°C in hot weather, 8 hours a day for 30 days. The last column is the extra on the bill of a home that uses 150 units without the AC (unprotected, 3 kW load, filer).

Inverter ACs use less because they slow the compressor down once the room is cool, instead of switching it fully on and off. On a very hot afternoon an inverter runs near full speed and uses close to a non-inverter's power; the saving comes over a whole day and night.

Worked example: 1.5 ton inverter, 8 hours a day

A family already uses 150 units a month without the AC. They run a 1.5 ton DC inverter at 26°C for 8 hours a day in a 30-day month.

1. Units per hour: 1,000 W = 1.0 unit.
2. Units per day: 1.0 x 8 = 8 units.
3. Units in the month: 8 x 30 = 240 units.
4. The bill goes from 150 units to 390 units. At 150 units the bill is Rs 7,290. At 390 units every unit is charged at the 301 to 400 slab rate and the bill is Rs 21,135.
5. Extra cost of the AC: Rs 13,845 a month, about Rs 58 per hour of cooling.

The same hours on a 1.5 ton non-inverter would use about 432 units and add Rs 27,147. Setting the inverter to 24°C instead of 26°C adds about 29 units and Rs 3,070. All bill figures use the tariff and adjustments in our electricity bill calculator.

Does the thermostat setting change the bill?

Yes. The table uses the rule of thumb published by India's Bureau of Energy Efficiency in 2019: each degree higher saves about 6% of an AC's electricity, and each degree lower costs about as much.

The reason is simple physics. Heat leaks into a room in proportion to the difference between inside and outside. At 40°C outside, a room at 24°C has a 16 degree gap; at 26°C the gap is 14 degrees, about an eighth less heat to remove. The 6% figure is an average and your own saving may differ, but the direction is certain. Most people are comfortable at 26°C with a fan running, and a ceiling fan uses less than a tenth of a 1.5 ton AC's power.

Why an AC can cost more than its own units

Unprotected homes pay one rate on every unit, set by the slab their total falls in. When an AC pushes a home from 150 units to 390 units, the first 150 units also move from the 101 to 200 rate up to the 301 to 400 rate. That is why the example above adds Rs 13,845 for 240 units, about Rs 58 per unit of AC use, well above the headline rate.

Protected homes lose protection above 200 units, and NEPRA's rules then keep them unprotected for six months. The calculator warns you if the AC does this. To see which appliances use the rest of your units, try the electricity usage calculator.

Where the wattage figures come from

An AC's nameplate shows its rated input power at the standard test condition, 35°C outside. What it actually draws depends on the weather, the room and the setting. The defaults here are typical running figures for Pakistani summers, the same ones used across our calculators. If you know your AC's own figure, from a plug-in meter or the rating plate, type it in.

For a non-inverter AC, count only the hours the compressor runs. On a 42°C afternoon that is nearly every hour; on a mild night it may be half. An AC that is too small for its room runs flat out all day, so check the size with the AC size calculator.

AC electricity questions