The exact calculation depends on grain temp, grain weight and water/grain ratio. My experience centers around 1.25 to 1.5 qts/lb with grain temps in the 60-70F range. Strike temp is usually somewhere around 165F with a preheated tun. So, it's like 15F higher. If the tun isn't preheated, it would be more like 178F. Download beersmith or beertoolspro for a free trial.