[bes]

<form action=" " method="post">
<input id="inp" type="text" name="rashod" size="6" align="center">
</form>	

и есть таблица

<table id="table" border="1" width="100%">
<tr>
<td> a x b , мм </td>
<script type="text/javascript">
for (k=50; k<=1000; k=k+50) 
document.write("<td>"+String(k)+"</td>");
</script> 
</tr>
<script type="text/javascript"> 

for (i=50; i<=1000; i=i+50)
{ 
document.write("<tr>"); 
document.write("<td>"+String(i)+"</td>");

for (j=50; j<=1000; j=j+50) 
{ 
var v=(i*j).toFixed(1);
document.write("<td>"+String(v)+"</td>"); 
}
document.write("</tr>"); 
} 
</script> 
</table>



<script>
window.onload = function () {
  var table = document.getElementById('table');
  var inp = document.getElementById('inp');
  var tr = table.rows;
  var len = tr.length;
  var td, tdLen;

  inp.onkeyup = function () {
    if (isNaN(inp.value) == false && inp.value != '') {
      for (var i = 1; i < len; i++) {//i = 0
        td = tr[i].cells;
        tdLen = td.length;
        for (var j = 1; j < tdLen; j++) {//j = 0
          //if (i == 0 && j == 0) continue;
          td[j].innerHTML = parseFloat(td[j].innerHTML) * parseFloat(inp.value);
        }
      }
    }
  }

}
</script>