TOG is a unit of measurements which evaluates the thermal resistance of a product. It's a worldwide standard and every Perlim pinpin sleep bag has been tested.
What to consider:
Each baby is unique. It is essential to think about his/her sleeping habits. How does baby usually wake up? Sweaty? With cold hands?
What is the highest temperature of the nursery through the night? Some families will lower the temperature to 19 degrees while others keep it at 22 degrees.
The TOG rating of each sleep sack is tested in lab. Unfortunately, is doesn't take consideration of the "feel" and "coziness" of all of our different fabrics. That's why each TOG is treated separately.