MySQL: определение размера таблиц
SELECT table_name AS table_name, engine, ROUND(data_length/1024/1024,2) AS total_size_mb, table_rows FROM information_schema.tables WHERE table_schema=DATABASE();

Показывает обьем и количество строк в таблицах MySQL.
Результат выглядит приблизительно так:


+<span class="comment">-------------------+--------+---------------+------------+</span>
| table_name        | engine | total_size_mb | table_rows |
+<span class="comment">-------------------+--------+---------------+------------+</span>
| categories        | MyISAM |          <span class="number">0.00</span> |         <span class="number">17</span> |
| downloadlinks     | InnoDB |         <span class="number">13.02</span> |      <span class="number">19158</span> |
| errors            | InnoDB |         <span class="number">15.02</span> |      <span class="number">84104</span> |
| lastdownloads     | MEMORY |          <span class="number">3.19</span> |        <span class="number">524</span> |
| providers         | MyISAM |          <span class="number">0.00</span> |         <span class="number">17</span> |
| starstags         | InnoDB |          <span class="number">1.52</span> |      <span class="number">14323</span> |
| tagids            | InnoDB |         <span class="number">35.59</span> |     <span class="number">759694</span> |
| tags              | InnoDB |       <span class="number">2036.00</span> |   <span class="number">21971934</span> |
| vars              | InnoDB |          <span class="number">0.02</span> |         <span class="number">51</span> |
| videocategories   | InnoDB |         <span class="number">49.58</span> |    <span class="number">1583675</span> |
| videos            | InnoDB |       <span class="number">1864.00</span> |    <span class="number">1954427</span> |
| videos_deleted    | MyISAM |         <span class="number">56.33</span> |      <span class="number">75889</span> |
| videostats2       | InnoDB |        <span class="number">271.88</span> |    <span class="number">3417776</span> |
| videostats2_daily | InnoDB |          <span class="number">0.02</span> |        <span class="number">266</span> |
+<span class="comment">-------------------+--------+---------------+------------+</span>

Правда есть один нюанс: на InnoDB-таблицах показывает количество незалоченных в данный момент строк.