<div>
<span id="spanCounter"></span>
<br />
<asp:TextBox ID="TextBox1" runat="server" Text="Sample Text"
onkeyup="spanCounter.innerText = this.value.length;"></asp:TextBox>
</div>
<div>
<span id="spanCounter"></span>
<br />
<asp:TextBox ID="TextBox1" runat="server" Text="Sample Text"
onkeyup="spanCounter.innerText = this.value.length;"></asp:TextBox>
</div>