4 cross would need longer spokes than 3 cross.
If one spoke crosses 3 others from the same side of the hub then it's a 3 cross.
Be careful doing 4 cross on high flange hubs with deep rims as the spokes cause weak points by crossing over the head of the previous spoke.
Also note that you can't do 4cross on 32h hubs.
4 cross would need longer spokes than 3 cross.
If one spoke crosses 3 others from the same side of the hub then it's a 3 cross.
Be careful doing 4 cross on high flange hubs with deep rims as the spokes cause weak points by crossing over the head of the previous spoke.
Also note that you can't do 4cross on 32h hubs.