How to best measure the performance of the web site while doing the testing either by any automation tool or by Manual Testing?

The performance of the site can be tested using JMeter by sending different kinds of load to the site and seeing if it works properly under stress. This load can be increased and decreased to find the optimum level of users who can concurrently use the website. 

By Automation tools like Jmeter or Load runner etc....

Performance testing is the best way to test the performance of a website. there are many performance testing tools available of which JMeter , RPT and HP Load Runner are the prominent ones. Both of them are easy to assess the performance of a website. the 'best' way obviously depends on the objectives of your project.

Again , there is a need to identify whether your project needs Performance Testing or Load Testing or Stress Testing.

Load Testing is simulating anticipated load, i.e. you have a requirement stating that system should support 500 concurrent users. So checking whether system will support 500 users providing reasonable response time and no errors is Load Testing.

Stress Testing is determining system boundaries and identifying the breaking point. So you start with 1 user and increase the load until errors start occurring or application response times exceeds thresholds whatever comes the first.

While Manually  testing is tedious as it is not possible to put a load of users at a time. May be you can do it with a stopwatch handy but it does not make any sense as we'll waste precious time available.

Jmeter really plays a vital role to test the performance of any web site.i think that you people know that the no of HTTP connections or con-current users are the causes of load of the web site and Performance can be best measured by using the Jmeter tool to calculate the load that is feeded to the websites

Jmeter helps generating loads (no of simultaneous users) which can help us to know the performance of application

For API testing we can user LoadUI to generate load and test API's

When it is performnce testing, Manually it is quite too difficult as it is not possible to synch many number of users at a time. Yes, you can check the performance for 1 user manually by a stop  watch but again the synch of your navigation and stop watch can be not at a time. 

It is always advisable to do with a automation tool such as HP load runner, Neoload , jmeter or IBM RPT etc. Where it will gives lot of option to create a real world scenarios for your script( nothing but your work flow or test case), execute it and lot of options to create your report as per the requirements.

But somepoints we need to be very carefull while doing the performance testing

1. Collect the requirement properly

2. Select all possible test cases that can impact the performnce

3. Select proper load mix as per your business, like banking, retail or telecom etc

4. Select proper network condition on which you want to test or what N/W the business is using

5. Select the different geography where the business operates, becoz the N/W, Latency vary from location to location

Automation Testing with Apache JMeter or LoadRunner or Rational Performance Tester or Loadstorm  

Automation should be best since various multiple inputs rather than manual can be given and verified simultaneously

We can verify the Functional part manually while the Load, Stress and Performance can be tested using automation tools liket JMeter, etc.

Automation Testing ,I would say HP LoadRunner is one of the best tool to measure the performance of an application.We can yes Jmeter for Performance now a day there are so many new tool developed for Automation.

By using JMeter or LoadRunner we measure the performance of a website.