ASP.Net RegularExpression Validators

Maximum character length Validation (Maximum 6 characters allowed)

<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:RegularExpressionValidator runat="server" ID="RegularExpressionValidator1"
Display = "Dynamic"
ControlToValidate = "TextBox1"
ValidationExpression = "^[\s\S]{0,6}$"
ErrorMessage="Maximum 6 characters allowed.">
</asp:RegularExpressionValidator>

Minimum character length Validation (Minimum 6 characters required)

<asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
<asp:RegularExpressionValidator runat="server" ID="RegularExpressionValidator2"
Display = "Dynamic"
ControlToValidate = "TextBox2"
ValidationExpression = "^[\s\S]{6,}$"
ErrorMessage="Minimum 6 characters required.">
</asp:RegularExpressionValidator>

Minimum and Maximum character length Validation (Minimum 2 and Maximum 6 characters required)

<asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>
<asp:RegularExpressionValidator runat="server" ID="RegularExpressionValidator3"
Display = "Dynamic"
ControlToValidate = "TextBox3"
ValidationExpression = "^[\s\S]{2,6}$"
ErrorMessage="Minimum 2 and Maximum 6 characters required.">
</asp:RegularExpressionValidator>

Alphanumeric with special Characters
Minimum length 7 and Maximum length 10. Characters allowed – a – z A – Z 0-9 ’@ & # .

<asp:RegularExpressionValidator ID="RegExp1" runat="server"
ErrorMessage="Password length must be between 7 to 10 characters"
ControlToValidate=" txtPassword "
ValidationExpression="^[a-zA-Z0-9'@&#.\s]{7,10}$" />

Alphanumeric Only
Minimum length 7 and Maximum length 10. Characters allowed – a – z A – Z 0-9

<asp:RegularExpressionValidator ID="RegExp1" runat="server"
ErrorMessage="Password length must be between 7 to 10 characters"
ControlToValidate=" txtPassword "
ValidationExpression="^[a-zA-Z0-9\s]{7,10}$" />

Alphabets Only
Minimum length 7 and Maximum length 10. Characters allowed – a – z A – Z

<asp:RegularExpressionValidator ID="RegExp1" runat="server"
ErrorMessage="Password length must be between 7 to 10 characters"
ControlToValidate="txtPassword"
ValidationExpression="^[a-zA-Z]{7,10}$" />

Numeric Only
Minimum length 7 and Maximum length 10. Characters allowed – 0 – 9

<asp:RegularExpressionValidator ID="RegExp1" runat="server"
ErrorMessage="Password length must be between 7 to 10 characters"
ControlToValidate="txtPassword"
ValidationExpression="^[0-9]{7,10}$" />

source:
http://www.aspsnippets.com/Articles/ASP.Net-Regular-Expression-Validator-to-validate-Minimum-and-Maximum-Text-Length.aspx