define número de elementos por colunas

category_itens_per_col.rb

# backend
def category_itens_per_col(total)
    return case total
      when 0..3 then 1
      when 4..6 then 2
      when 7..9 then 3
      else 4
    end
end

# frontend
- itens = category_itens_per_col(Category.count)
- Category.all.each_slice(itens) do |cs|
  .col
    - i = 0
    - cs.each do |c|
      %p{style:'padding:10px'}
        = set_spacing(i)
        %a{href: url_to_category(c), class: 'category_item', img: c.image.url(:regular)}= c.name
        - i+=1  

# css
.col
  margin-left: 60px
  display: inline-block
  vertical-align: text-top

set_spacing(3) => "   "