For existing customers with Dynatrace versions earlier than 1.198, your quota of existing custom metrics is automatically converted into DDUs (there's nothing you need to do to make this happen). New accounts (Dynatrace version 1.198+) will have DDUs per default and no conversion will be triggered.
A customer bought 500 host units and one volume of custom metrics (500 metrics). Each Dynatrace SaaS environment comes with 100 free custom metrics. Additionally, 10 free custom metrics are provided for each of your allotted host units. There is a maximum free tier limit of 10,000 custom metrics.
100 + 10 × 500 = 5,100 custom metrics + 500 paid custom metrics = 5,600 custom metrics
The DDU conversion only converts paid custom metrics, as we also include 1,000 metrics per host unit (Full-Stack Monitoring mode). For Infrastructure mode, we include 200 metrics. This means that 500 paid custom metrics equates to 262,800 DDUs per year. On top of this we provide an additional free tier of 200,000 DDUs. In total, you get 462,800 DDUs plus the 1,000 included metrics per host unit (in other words, bound to the host). Note that only the portion of existing custom metrics in this example is converted to DDUs. More conversion examples can be found in the table below.
Included metrics are bound to individual hosts.