Air-conditioner sizing

Air-conditioner is one of equipment that used and  popular in around the world to cooling our room,office or any space.Now in our market,air-conditioner have in many types and sizes.It depend on our application and types of space that we want use it.

When install an air-conditioner,we want it running in more efficiency and enough capacity can cooling the room.So we must install the right size for our room to ensure it suitable with room size and our application.

If we choose a smaller size for air-conditioner,it will running all the times to cooling the room.Your electricity bills will increase.But if you choose too big,it can kill you also with high electricity cost.So we need to choose a right size for air-conditioner.

Calculation for sizing an air-conditioner

Ok..this time i want share the simple basic of calculation how to sizing the air-conditioner.This is a critical part to ensure our selection is suitable with our requirement for room or any space that we want to cooling.

We must calculate the total heat for that room in unit Btu/hr.From this we can convert Btu/hr to air-conditioner size in horse power ( Hp ).We can estimate the size depend on horse power ( hp ).

Total heat calculation ( Btu/hr ) :

1) Measure your room or space area ( width x length ).Use a metric unit for measurement ( meter ).Multiply with 700 to get in Btu/hr

Example : Room area = 10 meter x 6 meter = 60 m2

Btu/hr = 60 x 700 = 42,000 Btu/hr

2) Estimate occupant for this room.multiply with 500 to get in Btu/hr

Example : 5 peoples x 500 = 2500 Btu/hr

3) Estimate the heat from electrical equipments such as lighting,television,computer,fax machine,radio or etc.Refer wattage for equipment and multiply with 3.5

Example : TV = 100 watt, Computer : 200 watt, lighting : 150 watt ; Total : 450 watt

so 450 watt x 3.5 = 1575 Btu/hr

4) So we add all answer to get a total Btu/hr.

Example : 42,000 Btu/hr + 2,500 Btu/hr + 1,575 Btu/hr = 46,075 Btu/hr

5) To get air-conditioner sizing, we must divide Total heat ( Btu/hr) with 9800 Btu/hr

* This value is depend on cooling capacity for each air-conditioner due to efficiency of compressor.It maybe 9,800 btu/hr,10,000 btu/hr or 12,000 btu/hr

Example : 46,075 / 9800 = 4.7 hp

6) From this answer we can estimate to choose a 5 Hp of air-conditioner for our room.

If you not sure to calculate air-conditioner size for your room,Please contact your local HVAC expert and the will calculate and advice the suitable size and types of air-conditioner for you.

This calculation is just for estimation value.It not absolute answer for your air-conditioner sizing.You can make a comparison your estimate air-conditioner size with your local HVAC expert.I hope this information can help all of you how to sizing the air-conditioner to avoid unnecessary cost.


  1. haitham hashim says:

    God bless you, I pray to God luck to you in this world and everlasting life, thank you

  2. haitham hashim says:

    Dear sir
    I have a query please, Do you mean 5 hp equal to 5 tons of cooling, when you convert a horse to TR using this equation, the theoretical ability horsepower required to rotate the compressor = TR * 0965. Is this what you mean, please, otherwise you can oath pregnancy macro-12000 alone temperature British / h and the result is = 4.70 tons of cooling as possible, please explain this paragraph with appreciation

    • hello haitham hashim,
      normally 1 hp of air-condition = 9,800 btu/hr,or if more efficiency it can get until 12,000 btu/hr for 1 hp of air-condition.please refer to manufacture catalog for the air-condition cooling capacity in Btu/hr.

      • haitham hashim says:

        Dear brother lemau Thank you for your answer and I personally will rely on this simple and beautiful, God bless you and I will wait for your articles kind,haitham hashim

  3. It is very useful,but the ambient temperature was not considered,why?.
    Similarly can you explain how to select suitable light fittings for
    a)living room 7mx12m-300lux
    b)office room 10mx20m-500lux
    c)low bay lighting for a warehouse 20mx40mx6mhigh-300lux
    If necessary recommend appropriate lux levels and do calculations

  4. I just used the same 60m2 area room in York Android application with 5 people and got 34791 Btu/h or 10kW. Could you please clarify your result – why 9800 btu/h = 1hp, many thanks.

    • Dear mr mark…the value is depend on your cooling capacity for your air conditioner.It cause by efficiency of compressor.It maybe 9,800 btu/hr,10,000 btu/hr or 12,000 btu/hr for 1 horse power.

  5. Where did you get the formulas you used for you computation? Thanks.

  6. Where did you get the formulas you used for your calculations? Thanks.

    • this formula is basic calculation for air-condition only can be used as a reference or guideline.For more detail please ask your local HVAC contractor. :D

  7. have to calculating area room how multiply 700 to btu/h

  8. How to check thermister

  9. damilola says:

    Thanks for the article it has been very useful but please why did we multiply the area of the room by 700(what does 700 signifies )? Secondly, the number of room occupants were multiplied by 500 (what does 500 signifies) ?thirdly, the rating of the room appliances were multiplied by3. 5 (what does 3.5 signifies?). Thanks a bunch

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