How to Measure your Boat Trailer Axle

(Even if It's Broken)

There are a lot of reasons you would want to know the measurements of your boat trailer axles. Maybe you just want to know everything there is to know about your towing setup (we get it, we're that way too). Maybe you want to make an upgrade to your capacity. Or maybe time (and salt water) has taken its toll and you need to replace an old or broken axle. To learn more about that process click here for our guide on boat trailer axle replacement–but before you do that, you'll need to know your measurements. So let's take a look at a few ways to do that.

Check for the Product Number

I know this one seems obvious, but it's important to mention it. Many axles will have a product number either on a sticker, a plate, or stamped into the metal itself. If you find this, you can look up the exact measurements on our site and you're good to go. It's seems simple, and it's pretty anticlimactic, but at least you don't have to roll around in the driveway!

If you're not one of the lucky ones, and your axle's product number is worn off or illegible, you're going to have to take some measurements. There are a few types of measurements you can take, and they aren't one-size-fits-all. So you may have to get a few before you can be 100% sure.

Note: We suggest removing your wheels if you are able while you take these measurements. It will be a lot easier.

axle sticker with product number circled

Look at this sticker–attached firmly, clearly legible (mostly), and all the information is there. You love to see it

Hub Face Measurement

This measurement is easily one of the most important ones to get when you're replacing your axle. Hub face measurement is taken from the outside edge of one hub face to the outside edge of the other (yes, it is important enough to bold twice).

Make sure you are measuring to the outside of each hub face

Spring Center Measurement

If there were one measurement that you wanted to get right, this one may be it. Making sure to accurately place the springs is extremely important so they don't make contact with the wheels or tires.

Hold your tape measure in the center of your leaf spring and measure to the center of the opposite leaf spring. This is notoriously difficult to do without a partner (especially if you're upside down underneath the trailer). So you can hook your tape measure on the outside edge of one spring, provided you're measuring to the inside edge of the other. This measurement should be identical to the center-to-center measurement.

Ideally you want to measure from the center of each spring

End-to-End Spindle Measurement

First and foremost it's important to say–this measurement isn't nearly as accurate as hub face and spring center measurements for selecting a new axle on its own. However, it's a good one to have for confirming that the axle you're purchasing is going to fit nicely on your boat trailer, or for helping select between a number of potential replacements.

For this measurement, you will go from the outside edge of one spindle to the outside edge of the other.

This measurement is good to get if you're torn between two or more axles and need to find the one that the most like the axle you're replacing

Measuring a Broken Axle

If you've been reading this article thinking to yourself "This all seems great, but what if my axle is in two pieces?" then don't worry, we didn't forget about you. Fortunately, the only thing we need here is a little creativity, and a little math (as if the broken axle wasn't bad enough already).

If you have a double, or triple-axle trailer, then you can just take the measurements of your other axle(s) and those will apply to the broken one as well. However, for single-axle trailers, we will have to do this in a few steps:

Locate the mounting brackets underneath your trailer (this is where the leaf spring attaches to the trailer)
Measure from the center of the mounting bracket on one side, to the center of the mounting bracket on the other. This will give you an estimate of your spring center measurement.
Now that you know your spring center measurement, go back to your broken axle and measure from the center of the leaf spring, to the outside edge of the hub face on the same side. We will refer to this as our leaf spring center to outside hub face measurement in the graphic below.
Take that measurement, multiply it by two (because this difference applies to both sides of the trailer) and add it to the estimated spring center measurement. This should equal (or at least be very close to) your hub face measurement! With that, and your spring center measurement, you're ready to select a replacement!

This diagram shows the measurements you will take on your axle to help show what we're measuring–and how those measurements add up with one another to make your hub face measurement

Measuring from the center of the mounting brackets on your trailer can give you a reasonable estimate of your axle's spring center measurement

So I Have my Axle Measurements–How do I Pick out a Replacement Axle for My Boat Trailer?

Congratulations! You will be relieved to know that the difficult part is over. Now you just need to head over to our selection of trailer axles and sort by hub face length and spring center length for plenty of options that will work for you, all sorted by capacity!

But we're not done yet, click here to read our guide about how to install your new axle on your boat trailer and let's get your boat back where it belongs, on the water!

About Jacob J

To say that my path to etrailer was complicated would be an understatement. I have always had a passion for helping others, and throughout my education and career as a social worker or community liaison, I have loved writing as a hobby. When I found etrailer and was given the opportunity to turn something I enjoyed doing into a career that helped people access information and products they need to live the best life they possibly could, I was instantly interested.

I am a lover of the outdoors, I have been loading and unloading trailers since before I was old enough to drive them, and have spent my recent years working in and around the automotive industry. And I am excited to share all of the things I have learned (more often than not the hard way).

I consider myself a perpetual student, and etrailer gives me the opportunity to learn something new every day and share my findings with others. Which is something I am extremely grateful for. I look forward to continuing to help people find the answers they need to make memories for a lifetime.