This macro will return read time in human readable format, adjusted to your site locale. More info: http://craftsnippets.com/articles/read-time-macro-for-craft-cms

read_time_macro.twig

{% macro readTime(text) %}
{% spaceless %}
{# v1 #}
    {# settings #}
    {% set wordsPerMinute = 265 %}
    {% set showLessThanMinute = true %}
    {# logic #}
    {% set plaintext = text|striptags|replace({'—': ' ', '–': ' ', '-': ' ', '\n': ' '}) %}
    {% set words = plaintext|split(' ') %}
    {% set minutes = ceil(words|length / wordsPerMinute) %}
    {% set seconds = minutes * 60 %}
    {% set formatter = create({ class: 'craft\\i18n\\Formatter' }) %}
    {% if (words|length / wordsPerMinute) * 60 < 60 and showLessThanMinute %}
        {{'less than'|t ~ ' ' ~ formatter.asDuration(60)}}
    {% else %}
        {{formatter.asDuration(seconds)}}
    {% endif %}
{% endspaceless %}
{% endmacro %}