That is 1 Satoshi is $0.00085389. Example. The current price of Bitcoin $85, 389 divided by 100,000,000 ( $85,389 ÷ 100,000,000 = 0.00085389). Therefore if you are paid 5000 Satoshi per post, you will times (x) it with the final results which is 5000 Satoshi x 0.00085389 = $4.26945 then you times (x) it again and to the total post of the week. Which might be 20 posts. $4.26945 x 20 = $85.389.
That is the simple manual calculation. Many of us especially our newbies get confused if they here mBTC, sats, and even micro BTCs; but for simple calculations, using 1BTC as reference.
1BTC = 0.0001 mBTC that is by deciding by 1000 as you had explained.
For easy understanding especially for some of us who finds it difficult using calculators to calculate it, we can use some tools like that of Bitmover as stated above, and other tools you can see online. They are useful and makes it looks easy to access and knows the value using different units.
You can visit these tools
This tool, and also
this tool.