Calculate how many chairs can fit into the auditorium, allowing for gangways and any pillars that may block someone's view. Consider the width of each chair and the leg space allowed for each person. Take into account chairs that join together (as in cinemas), which could be preferable to use since they save space.
Check that the number of chairs that will fit is enough to accommodate the number of people attending the event. Create a diagram using CAD software or Microsoft Word, using shapes for the auditorium and chairs, to obtain an idea of the layout using the visual aid.
Check Health and Safety regulations regarding gangways and leg space to ensure you have left enough room for both. Mark up any area that is going to be reserved for VIPs or people who have to sit at the front.
Allow for wheelchairs and disabilities. Find out how many people may be attending in wheelchairs and if they are bringing caregivers, as this will require more room per wheelchair than a normal chair would take up.
Go to the auditorium and layout some chairs to ensure your calculations are correct. Double check all of your calculations. Order the chairs in well in advance of the event. Organize assistance to help you lay out the chairs once they arrive.