WinForm: Get available caption size

Form1.cs

using System;
using System.Drawing;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            UpdateStats();
        }

        private void UpdateStats()
        {
            var availableWidth = CalcAvaliableCaptionWidth();
            var textWidth = TextRenderer.MeasureText(captionTextTextBox.Text, SystemFonts.CaptionFont).Width;

            availableSpaceTextBox.Text = availableWidth.ToString();
            captionTextWidthTextBox.Text = textWidth.ToString();

            statusPanel.BackColor = (textWidth > availableWidth ? Color.Red : Color.Green);
        }

        /// <summary>
        /// Calculates an approximation of the available caption width
        /// Depends on OS and theme
        /// </summary>
        /// <returns>Width</returns>
        private int CalcAvaliableCaptionWidth()
        {
            return
                // Form width
                Width
                // Icon
                - (Icon == null ? 0 : Icon.Width)
                // Minimize button (26 on Win8)
                - (MinimizeBox ? SystemInformation.CaptionButtonSize.Width : 0)
                // Maximize button (26 on Win8)
                - (MaximizeBox ? SystemInformation.CaptionButtonSize.Width : 0)
                // Close button (45 on Win8)
                - SystemInformation.CaptionButtonSize.Width;
        }

        private void captionTextTextBox_TextChanged(object sender, EventArgs e)
        {
            Text = captionTextTextBox.Text;
            UpdateStats();
        }

        #region Windows Form Designer generated code

        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if(disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.captionTextTextBox = new System.Windows.Forms.TextBox();
            this.label1 = new System.Windows.Forms.Label();
            this.label2 = new System.Windows.Forms.Label();
            this.availableSpaceTextBox = new System.Windows.Forms.TextBox();
            this.label3 = new System.Windows.Forms.Label();
            this.captionTextWidthTextBox = new System.Windows.Forms.TextBox();
            this.statusPanel = new System.Windows.Forms.Panel();
            this.label4 = new System.Windows.Forms.Label();
            this.SuspendLayout();
            // 
            // captionTextTextBox
            // 
            this.captionTextTextBox.Anchor = ((System.Windows.Forms.AnchorStyles)(((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Left)
            | System.Windows.Forms.AnchorStyles.Right)));
            this.captionTextTextBox.Location = new System.Drawing.Point(12, 31);
            this.captionTextTextBox.Name = "captionTextTextBox";
            this.captionTextTextBox.Size = new System.Drawing.Size(294, 20);
            this.captionTextTextBox.TabIndex = 0;
            this.captionTextTextBox.TextChanged += new System.EventHandler(this.captionTextTextBox_TextChanged);
            // 
            // label1
            // 
            this.label1.AutoSize = true;
            this.label1.Location = new System.Drawing.Point(12, 15);
            this.label1.Name = "label1";
            this.label1.Size = new System.Drawing.Size(87, 13);
            this.label1.TabIndex = 1;
            this.label1.Text = "Your caption text";
            // 
            // label2
            // 
            this.label2.AutoSize = true;
            this.label2.Location = new System.Drawing.Point(12, 54);
            this.label2.Name = "label2";
            this.label2.Size = new System.Drawing.Size(123, 13);
            this.label2.TabIndex = 3;
            this.label2.Text = "Available space (approx)";
            // 
            // availableSpaceTextBox
            // 
            this.availableSpaceTextBox.Anchor = ((System.Windows.Forms.AnchorStyles)(((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Left)
            | System.Windows.Forms.AnchorStyles.Right)));
            this.availableSpaceTextBox.Location = new System.Drawing.Point(12, 70);
            this.availableSpaceTextBox.Name = "availableSpaceTextBox";
            this.availableSpaceTextBox.ReadOnly = true;
            this.availableSpaceTextBox.Size = new System.Drawing.Size(294, 20);
            this.availableSpaceTextBox.TabIndex = 2;
            // 
            // label3
            // 
            this.label3.AutoSize = true;
            this.label3.Location = new System.Drawing.Point(12, 93);
            this.label3.Name = "label3";
            this.label3.Size = new System.Drawing.Size(71, 13);
            this.label3.TabIndex = 5;
            this.label3.Text = "Caption width";
            // 
            // captionTextWidthTextBox
            // 
            this.captionTextWidthTextBox.Anchor = ((System.Windows.Forms.AnchorStyles)(((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Left)
            | System.Windows.Forms.AnchorStyles.Right)));
            this.captionTextWidthTextBox.Location = new System.Drawing.Point(12, 109);
            this.captionTextWidthTextBox.Name = "captionTextWidthTextBox";
            this.captionTextWidthTextBox.ReadOnly = true;
            this.captionTextWidthTextBox.Size = new System.Drawing.Size(294, 20);
            this.captionTextWidthTextBox.TabIndex = 4;
            // 
            // statusPanel
            // 
            this.statusPanel.Location = new System.Drawing.Point(12, 148);
            this.statusPanel.Name = "statusPanel";
            this.statusPanel.Size = new System.Drawing.Size(294, 40);
            this.statusPanel.TabIndex = 6;
            // 
            // label4
            // 
            this.label4.AutoSize = true;
            this.label4.Location = new System.Drawing.Point(12, 132);
            this.label4.Name = "label4";
            this.label4.Size = new System.Drawing.Size(90, 13);
            this.label4.TabIndex = 7;
            this.label4.Text = "Fit status (approx)";
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(318, 200);
            this.Controls.Add(this.label4);
            this.Controls.Add(this.statusPanel);
            this.Controls.Add(this.label3);
            this.Controls.Add(this.captionTextWidthTextBox);
            this.Controls.Add(this.label2);
            this.Controls.Add(this.availableSpaceTextBox);
            this.Controls.Add(this.label1);
            this.Controls.Add(this.captionTextTextBox);
            this.Name = "Form1";
            this.Text = "Form1";
            this.ResumeLayout(false);
            this.PerformLayout();

        }


        private System.Windows.Forms.TextBox captionTextTextBox;
        private System.Windows.Forms.Label label1;
        private System.Windows.Forms.Label label2;
        private System.Windows.Forms.TextBox availableSpaceTextBox;
        private System.Windows.Forms.Label label3;
        private System.Windows.Forms.TextBox captionTextWidthTextBox;
        private System.Windows.Forms.Panel statusPanel;
        private System.Windows.Forms.Label label4;

        #endregion

        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}