Are there any best practices for estimating web traffic based on an estimated user base?

I personally have had success with the Google Keyword Finder. This is part of the Google Adwords program for estimating keyword traffic and since Google has statistics on everyone's surfing and search habits, this is your best bet.

My advice to you is that before you try estimating server traffic for your marketplace, select 5 to 10 short and long tail keywords that you want to target and then use Google's Keyword Finder to look at the search traffic.

I hope this helps.
Bruce

One of the machines where I host client sites has been receiving 250,000+ uniques/hour every day for months.

Monthly lease on this machine is <$200 USD/month.

It's more how well your LAMP Stack is tuned, rather than your hardware.

LAMP Stack - Linux + Apache + MariaDB (working MySQL) + PHP + Openssl + CMS (like WordPress) + theme + plugins.

Well tuned + cheap hardware performs far better than poorly tuned hardware with unnecessary bolt ons - CDNs + NGINX + Varnish + Load Balancers (to name a few).

Hire a competent site designer (someone who understands end-to-end site design + LAMP tuning) + likely you're server hardware will be run of the mill.

I personally use OVH for my provisioning. They provide hardware + terminal server interface (for crash recovery) + nothing else. No OS. Nothing else.

A good site designer can turn OVH raw hardware into blazing fast sites.

Here is some step, by following these steps u can easily measure the website traffic.
Step 1:
Sign up for a website traffic-measuring service. Google Analytics is a popular free service that tracks and measures a website's performance in traffic.
Step 2:
Add the service's tracking code to your webpages. Your traffic-measuring service may provide code for you to copy and paste into the code of your webpages.
Log in to your account if necessary. Follow the service's instructions to find your tracking code, which may be located through your account profile.
If you used a template to build your site, you may only need to paste the tracking code 1 time into the template's file to apply the code to all your webpages.
Try adding the code right before the closing "head" tag, marked by a slash (/) before the word "head." You may need to add the code just before the closing "body" tag of a web page's HTML code instead.
Check that you added all of the tracking code correctly to your webpage(s).
Step 3:
Look at a report(s) for your website's traffic. The report(s) may be known as website metrics report(s). You may need to wait a day or so for the code to gather data for the report(s) from tracking those who visit your site and their associated information and activity on your site.
Log into your tracking service's account if necessary. Access your report(s) as directed by the service website.
Examine the statistics that your report(s) measure. These may include the number of unique visitors you have had, what links your site's visitors clicked on, and what page they landed on from a search engine.
Step 4:
Use a website traffic counter as an alternative. A website traffic-measuring site such as StatCounter may offer a counter for people to display on their sites.
Register for an account at the counter's website if necessary.
Copy and paste code for the counter in the website's code.
If offered, choose which statistic to display in your counter. Examples could be the number of times the counter's webpage is viewed (page load or page views) or how many unique visitors your site is receiving.
Customize your counter if applicable. You may be able to choose how many digits your counter can show, what color or font the counter is displayed in, etc.

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