as stated.~ :-p

Select the Portal and then - Select View > Object size. Click the in/cm/px until it turns to px. Then you can either ...

Click on the portal and divide the total number displayed in the px by the number of rows. This tells you the row height.

Easier way ... change your portal to one row. This gives you the row height. You can then change the bottom number (object height) to whatever you wish - one px at a time; then change your portal row numbers back.

You can also drag the portal row but I've found this to be difficult to implement with precision.

thank you~