If you are talking about an irregular shape like this, the correct term would be perimeter. Circumference is reserved for the perimeter of circles.
But to answer your question, the perimeter would be the circular lengths, not the square. You have 4 half-circles which have a perimeter equal to two circle circumferences.
One circle:
C = 2π r
Two circles:
2C = 4π r
And r is 2 cm.
Answer:
8π ≈ 25.1328 cm
