If you do not have prior peak traffic data, if your site has low visitorship, and has content that could go viral, account for peak traffic that can be up to 30 times your average daily traffic.
If your site has high and stable visitorship, peak traffic can be up to 5 times your average daily traffic.
If you have prior peak traffic data and timing of peak traffic is predictable (seasonal traffic and controlled traffic spikes), use past data and add a percent growth in traffic to arrive at the final number.
Posted from Diigo. The rest of my favorite links are here.