A tempo run is designed to challenge your threshold and get your body used to sitting on that pace. Technically it should be the pace that your body is creating lactate at the same rate it is able to get rid of it, so it should feel hard but mostly comfortable. The brilliance of a wave tempo is that by moderately overloading your threshold and then only allowing minimal recovery you are going to see some improvements in your threshold that you wouldn’t see in a steady state run.
Ideally you would want your steady pace to be 5% slower than tempo and your fast pace to be 5% faster. This is just a guide:
3:30 Tempo (3:20 min/km fast, 3:41 min/km steady)
4:00 Tempo (3:49 min/km fast, 4:13 min/km steady)
4:30 Tempo (4:17 min/km fast, 4:44 min/km steady)
5:00 Tempo (4:46 min/km fast, 5:16 min/km steady)
5:30 Tempo (5:14 min/km fast, 5:47 min/km steady)
6:00 Tempo (5:43 min/km fast, 6:19 min/km steady)
6:30 Tempo (6:11 min/km fast, 6:51 min/km steady)
7:00 Tempo (6:40 min/km fast, 7:22 min/km steady)
7:30 Tempo (7:09 min/km fast, 7:54 min/km steady)
8:00 Tempo (7:37 min/km fast, 8:25 min/km steady)
8:30 Tempo (8:06 min/km fast, 8:57 min/km steady)
9:00 Tempo (8:34 min/km fast, 9:28 min/km steady)
If you are more comfortable with a 3km distance as opposed to a 6km run – just change the intervals to 500m instead of 1km.