60-second answer
Calculate the profit target first, then multiply by 100.
Find the maximum acquisition cost after variable order costs and retained profit. Divide the conversion-value basis by that amount to get target ROAS in x format. Multiply by 100 for Google Ads percentage format.
Google tROAS % = (conversion value / allowable ad spend) x 100
For example, 2.86x is entered as 286%. A 286% bid target does not mean Google will produce exactly 2.86x actual ROAS or preserve order volume.