Here are the measurements of our last for every model. You should consider some free space in the front part of the boot.
Usually, we recommend adding 7-10 mm, so for a foot of 27 cm we would recommend the size 42. However, if you wear some thicker socks in the winter or if you have very wide feet, you might want to go for the 43.
Some people prefer a tighter fit, and some people like it a bit looser.
The best way we found that works for everyone is to measure your feet. The more precise you can get, the most correct size we can recommend.
HOW TO MEASURE YOUR FOOT:
1. Put your foot on a paper.
2. Circle the foot around holding the pen 90 degrees with the floor.
3. Measure the distance from the longest toe to the heel.