# What’s The Difference Between Arrival Rates and Inter Arrival Times?

We have a really great tip for you today. We’ve heard that sometimes users get confused between arrival rates and inter-arrival times.

Well, let’s clarify this for you; the inter arrival time is a key option in the Start Point of any simulation, therefore it’s really important that users know the difference before they start simulating.

• The arrival rate is the number of arrivals per unit of time.
• The inter arrival time is the time between each arrival into the system and the next.

The arrival rate is calculated from the following equation;

arrival rate = 1/inter arrival time

The neat trick with this equation is that if you invert the arrival rate your answer is the inter arrival time which can then be used in your simulation.

inter arrival time = 1/arrival rate

For example;

If 12 customers enter a store per hour, the time between each arrival is;

inter arrival time = 1/arrival rate

= 1/12

= 0.083 (hours)

= 0.083 x 60 minutes

= 5 (minutes)

Therefore from the arrival rate of 12 per hour, the time between each arrival is 5 minutes.

We hope you found this tip useful!!