This new square is the same size as the Firetruck 40 (which means it begins with 40-windows when using the interlocking technique, chart size of 81 x 81); see more of this size listed here: ashleeslint.com/patterns#large
When using worsted weight yarn and meeting my gauge you should get a finished square of about 20″ / 50cm.
You can create a large border to get a small baby blanket or join it to some more squares and make a blanket! It is easiest to use squares of the same size but you can also mix and match (the Dumptruck 20 square might work with this one?).