This handy chart will help you find your swimming RPE zones.
To determine your STP (Swim Threshold Pace), you will need to complete the 50/500 swim test found in the multisport test week plan. The calculation is as follows:
Add 25 seconds to your total 500m swim time, then divide that number by 5.
This will give you your STP in terms of time per 100m. Your zones will then be based on adding or subtracting from that 100m pace.