Over the past two years we have stayed in several hotels. We have always questioned how much we should tip. After doing some research we found that you should tip $3-$5/day or $5-$10/day depending on where you stay. The nicer the place, the more you tip. The higher end hotels typically have more staff and offer more services, therefore, you want to tip more.
Check out this article by Huff Post
https://www.huffpost.com/entry/tip-hotel-housekeepers-every-day_l_61796c96e4b0657357438814/amp