Macro truncating text by the number of words. More info: http://craftsnippets.com/articles/truncating-text-with-twig-macros-in-craft-cms

truncate_words.twig

{# v1 #}
{% macro truncateWords(text, length, suffix) %}
{% spaceless %}
{# settings #}
{% set defaultSuffix = '...' %}
{# logic #}
{% if text and length %}
{% set suffix = suffix|default(defaultSuffix) %}
{% set text = text|striptags %}
{% set text = text|replace('/\\n/', '\n ') %}
{% set array = text|split(' ') %}
{% set arrayTruncated = array|slice(0, length) %}
{% set string = arrayTruncated|join(' ') %}
{% if array|length > length %}
    {% set string = string ~ suffix %}
{% endif %}
{% set string = string|replace('/\\n\\s/', '\n') %}
{{ string }}
{% endif %}
{% endspaceless %}
{% endmacro %}