Measuring Sails - Easy How to Guide

Getting Started

Choosing and ordering new sails should be exciting. It's a chance to think about how you sail, where you sail, and what you want from your boat.

As you browse our website, you'll see a variety of sail options and features. Take some time to explore what's available and think about what matters most to you. If you have questions, we're always happy to help.

A great first step is to complete the "Get a Quote" form on our website. Include any questions or special requirements, and we'll help guide you through the process.

Rig Dimensions vs. Sail Dimensions

When requesting a quote, you'll be asked for several rig measurements: I, J, P, and E. These measurements aren't the actual sail dimensions, but they give our sail designers the information they need to create sails that fit your boat properly.

You can measure these dimensions yourself, find them in your boat's documentation, look them up on websites such as SailboatData, or copy them from a current racing certificate if you have one.

Here's what they mean:

I – Height from the deck to the point where the headstay attaches to the mast.
J – Horizontal distance from the front of the mast to the headstay attachment point on deck.
P – Maximum mainsail luff length, usually measured between the black bands on the mast.
E – Maximum mainsail foot length, usually measured between the black bands on the boom.
PY and EY – Similar measurements for the mizzen sail on ketches and yawls.

Basic Sail Terminology

A few common sail terms you'll see:

Luff – The front edge of the sail.
Leech – The back edge of the sail.
Foot – The bottom edge of the sail.
Clew – The aft lower corner of the sail.

For headsails such as jibs and genoas, you'll also hear the term LP (Luff Perpendicular). This measurement determines how much the sail overlaps the mast.

That's where terms like "130% genoa" come from. A 130% genoa overlaps the mast by approximately 30% of its LP measurement, while a 100% jib has little or no overlap.

If these terms seem confusing, don't worry. As long as the measurements are accurate, our designers will make sure the sail is designed correctly.

Measurement Tools

Mainsail Measurement

Headsail Measurement

Downwind Sail Measurement

How to Measure Your Boat

Taking measurements is a straightforward process. It doesn't require special skills—just a little patience and attention to detail.

You'll need:

A long, flexible tape measure with a loop on the end for attaching to a halyard
A calm, dry day with light wind
Enough time to work carefully

For example, a 37-foot boat may require measurements over 48 feet long, so make sure your tape measure is long enough.

Measuring the Rig vs. Measuring Old Sails

While you can measure your existing sails, measuring the rig is always the better option.

Older sails may have stretched, shrunk, or become distorted over time. They also may not have been designed optimally when they were originally built. If you do decide to measure your sails, then the best option is to measure them on the boat hoisted with proper halyard tension. Old sails will typically shrink in the luff when you measure on the ground, but as soon as it is put under halyard tension it stretches back out.

Measuring the rig gives us the most accurate information and allows us to design sails specifically for your boat.

Helpful Tips

Check Your Tape Measure

Before you start, make sure the zero mark is actually at the end of the tape. Some tape measures have loops or fittings that can affect the starting point of the measurement.

Use a Downhaul Line

Whenever you hoist a tape measure on a halyard, tie a separate downhaul line to the halyard as a backup.

If the tape breaks or comes loose, you'll still be able to retrieve the halyard without sending someone up the mast.

Pull the Tape Tight

For accurate measurements, always keep the tape measure under tension. A loose tape can introduce errors.

Measure Twice if Needed

If a measurement seems questionable, take it again. It's better to provide multiple measurements and notes than to rely on one reading you're unsure about.