IMPORTANT: Measure your rig's maximum dimensions. Our sail designers will make the proper allowances for stretch and hardware.  
"I" dimension: Attach a tape measure to the jib halyard or (roller-furling only) to the lower shackle of the upper furling unit and hoist the halyard up as high as it will go. Record the distance from the peak to the headsail tack fitting or (roller-furling only) the tack shackle of the furling drum.
"J" dimension: Furling and non-furling sails: Measure from the stemhead (NOT the furling drum) to the front face of the mast at deck level.
  On most cruising boats, the jib or genoa, even if it is smaller than the mainsail, contributes most of the drive when sailing to windward or reaching. Along with low-stretch sailcloth and a well-designed airfoil shape, important considerations when considering a headsail are cloth weight and overlap. For all-around cruising, a 130% to 150% overlap (overlap = % of the "J" dimension) is fine. Our sail designers can assist you in determining the correct overlap and fabric weight for the type of sailing you plan to do.
  We offer five types of headsail panel layouts, each suited to particular type of cruising and length of boat. If you are uncertain which panel layout is best for your needs, we are happy to offer our advice. Just enter your questions on line 10 or in the "Your Headsail Particulars" section of the Get a Quote form.

An all-purpose panel layout for small to mid-size boats, the crosscut is versatile. Crosscut fabrics are well-proven, stable, and available in many weights.
Best for small to mid-size boats, the vertical cut eliminates load-bearing seams along the leech. Durable for long-term use.
Best for boats over 40 feet. The tri-radial design reduces sail stretch and allows the use of "step up" fabric weights to handle high loads while saving weight in low-load areas.

Good for small performance cruising boats and mid-size cruising boats. The bi-radial design reduces stretch and allows "step up" cloth weights for easy handling.
A cost-effective radial panel layout for smaller boats. Maintains its radial-design low-stretch ability when deeply roller-reefed.
  At Hong Kong Sailmakers we do not use racing fabrics - they are too stiff for easy handling, and their service life is not up to our standards. We do, however, work closely with our fabric suppliers, and we demand the best cruising fabrics with the following characteristics: 1. High-tenacity (high-quality) polyester yarns; 2. Tightest possible weave; 3. Low stretch along the threadline and across the bias direction; 4. Softest possible resin finish for easy handling. Given the volume of sails that we've built over the past 20 years, our suppliers are happy to meet our requirements!
  If you are considering a furling headsail, we offer two choices of leech and foot suncover: acrylic Sunbrella and UV-protected Dacron, both available in a range of colors. We recommend a foam luff flattener if you plan to sail with your sail roller-reefed; a foam luff will considerably improve the reefed airfoil shape of your headsail.