You obviously need sufficient power supply to ensure that all the electrical appliances in your restaurant are able to function simultaneously. As a general guideline, a typical restaurant will need atleast about 20 KVA power. 1 KVA is approximately equal to .8 KW.
The big power consumers are the following:
1) The Kitchen Exhaust System: The exact power requirement would depend on the motor capacity and the efficiency of the motor used. The capacity (power generated) would depend on whether the blower is kept right next to the exhaust hood in the kitchen or taken all the way to the terrace of the building. Most small restaurants will typically need a 2 HP or a 3 HP motor powering the exhaust system blower. 1 HP is approximately equal to .75 KW and assuming a motor efficiency (this is the efficiency of converting electrical power to mechanical power) of 50%, you will need 1.5 KW for every 1 HP. So a 3 HP motor (the most commonly used motor at restaurants) will need about 5 KVA power. Once running the motor may not consume as much power as the motors need an extra power surge during start-up.
2) Air-Conditioners: Depending on the number and type of ACs you install, you will need to calculate your power requirement. A typical 1.5 Ton Split AC will need about 2 KVA of power supply.
3) Freezers/Chillers/Water Coolers: The exact power requirement for these appliances are typically mentioned in the back of these appliances. As a guideline, most freezers and chillers need about 300-500 KVA of power supply.
4) Mixers, Grinders, Microwaves, Ovens, Electric Stoves, Beaters, Water heaters etc.: These small appliances you will use in the kitchen are large power consumers. Most of them need between 1 KVA and 2 KVA of power. Depending on the items you use in the kitchen, you will need to calculate your power requirements. For a typical restaurant you won't use all of these items at the same time - so can assume you will need about 2-4 KVA for these small kitchen appliances.
5) Lighting, Sign Boards, Billing System etc.: You will notice that most restaurants use low power consuming CFL lights and LEDs. As a guideline, you should budget about 1-1.5 KVA power for all your lighting, fans, sign-boards, computer/billing system and other small electrical stuff in the restaurant. If you use a Neon sign-board, the power needed will be higher (budget an additional .5 KVA atleast)
Let's now take an example of a 2000 sft air-conditioned restaurant, with 4 split ACs of 1.5 Ton capacity each and a exhaust system with a 3 HP motor. The table below shows the calculation of the total power requirement for this restaurant. You will need to compute the power requirement for your restaurant based on the exact items you will need and will be using.