I have one solution for you.
This code will show and unordered list with the name of the category and the count of posts containded in it.
<ul class="myClass">
<?php $categories = get_categories('number=100');
foreach ($categories as $cat) {
echo "<li>". $cat->cat_name . " Total posts: ". $cat->category_count ."</li>";
} ?>
</ul>
Retrieves the 100 first categories
$categories = get_categories('number=100');
and for each of them shows cat_name
and category_count
Well the result I presume you really need can now be handled in a var by $cat->category_count
, i.e:
$total_num_posts_in_your_category = $cat->category_count
I hope that could help you.