different tools show different rankings

[sarahemi]

I am here for a query about my sites overall SERP rankings and a little bit confused about why different tools like SEMRush, AHrefs, Alexa, SEO Small Tools, MAjestic etc show totally different site rankings.
As I am using Ahrefs for a year for my SEO operations and my ranking was beyond 10000000+ and now after its SEO working, I managed to bring it to 500000 in between. But when I checked rankings into Alexa, it shows rank between 8000000-9000000 rankings. I thought that two different tools could not be 100% same in showing rankings but such a great difference is really strange.

[damponting44]

A ranking is a relationship between a set of items such that, for any two items, the first is either 'ranked higher than', 'ranked lower than' or 'ranked equal to' the second
SEO ranking sites are:

Moz Local Listing Score. ...
Keywordtool.io. ...
Google Analytics. ...
Google Webmaster Tools + Bing Webmaster Tools. ...
Open Site Explorer. ...

[damponting44]

1. Ahrefs
2.SERPWatcher
3. Google Rank Checker
these are the different ranking tools  and which shows the different raranking for different sites.