How To Measure A Bolt Pattern

What is the bolt pattern on your trailer wheels?  For the most part it doesn’t matter because you’re not changing wheels that often, yet when it does matter, it really matters.  Here is some good info to measure and calculate just what that bolt pattern is.

There are actually a bunch of different hole combinations for connecting the wheels on cars, trucks and trailers.  The set of holes for the bolts attaching the wheel to the axle is the “Bolt Pattern”.  While it’s not usually a concern, if you get new wheels, it’s important so the new wheels fit.  If the pattern is wrong, then of course, the wheel is not of much use.

Another detail, if you ever wonder about load capacity of an axle, the bolt pattern can tell you something.  It’s not exact, but in combination with other info, it may tell you something.

Terms For A Bolt Pattern

When trying to identify a specific bolt pattern, there are some descriptive terms worth knowing.  Here are some phrases to remember (with the image to reference).Dimensions in a Bolt Pattern

  • Bolt Pattern — The set of holes, or more exactly, the combination of holes and locations for the bolts attaching the wheel to the axle.  This includes the number N of bolts.
  • Bolt Hole Size — The size of the holes the bolts pass through, or really, the size of the bolts.  The holes will be larger than the actual bolt diameter, but not by a lot.
  • BCD, or Bolt Circle Diameter — When the bolts are in a circle around the center of the wheel, the diameter of that circle is the BCD, or Bolt Circle Diameter.
  • Hub Diameter — Size of the hub, or really, the size of the hole in the center of the wheel.  The axle hub passes through this hole when the wheel goes on.
  • Distance Between Bolts — (actually, Distance Between Adjacent Bolts) — A measurement of the distance from the center of one bolt, to the center of the next.  That is called “center-to-center” as well.

While there are a lot more terms to describe a wheel, we covered many of them in our Wheels and Tires article.   That’s a good one to read as well for more info.  However, in this article we’re going to focus on the bolt pattern.

Standard Patterns

A very common way to refer to the various bolt patterns is “the number of bolts” on a “bolt circle diameter”.  Something like 5 on 4.5 — meaning 5 bolts on a 4.5″ diameter circle.  It’s a short-hand reference, but it does the job in communication.

Some of the more common sizes for bolt patterns include:  4 Bolts on 4″ Diameter,  5 Bolts on 4.5″ Diameter,  6 Bolts on 5.5″ Diameter,  and 8 Bolts on 6.5″ Diameter.  There are several others like 5 on 5 that do show up, but they are less common.  Hey, there’s even some 10 bolt patterns for the heavy ones.

Use this nomenclature when you’re shopping for wheels.  It helps a lot knowing the terms.  Here are some visual examples.  Note that the hub hole also get’s larger as the number of bolt holes increases.  That center hole also has some standards, but that is not something you need to know to order wheels.

Pick Your Bolt Pattern

Though it’s not specifically mentioned for most bolt patterns, the size of the bolt also matters.  Most are 1/2″-20 threads, but check just to verify.  Here’s another article with more info about trailer wheel lug nuts and lug bolts.

Identifying A Wheel Bolt Pattern

How do we measure?  When you have an even number of bolts, you can often measure directly across the wheel for opposite bolts to get the Bolt Circle Diameter (BCD).  That seems easy enough, but what if the wheel is mounted and the hub is in the way?

For odd numbers, or when the hub is in the way, it’s not that easy to directly measure.  So, calculate it.  Here’s the equation that gives an exact result based on a simple bolt to bolt measurement.  (Hole to hole works too.)


Since measurements are not always perfect, just do the calculation and round a little to the bolt pattern that makes most sense.  For instance, a 5 bolt pattern is not likely to be 5 on 4.467″, but we know that a common pattern is 5 on 4.5″, so round a little, and you’ve got your answer.

Before worrying about equations, remember, the easiest way to get BCD for a bolt pattern with even numbers of bolts is direct measurement.  Strait across from one bolt or hole, to the opposite bolt or hole on the other side of the hub.  There are only a few standard patterns, so you don’t have to be super exact in measuring.

If you don’t want to calculate, use this table.  Here are a few of the common patterns and the theoretical perfect distance between the bolts.

Look Up Table

More Reading

For odd bolt patterns — like 5 bolts — in the size we’re talking about for trailer wheels, there is a cheat method that mostly works.  As an engineer, I like the direct methods above, but this measuring trick is worth knowing.  It’s not exact, but it gets close — well, for these specific circumstances.

We have a few more articles on the subject of Axles, Wheels, and Tires.  First, the Trailer Axles 101 article for an overview of axles in general.  Next, the article reference above for Trailer Wheels and Tires — which is about the tire specifications.  Just add the above information to the Specs for your wheels and you’ll have the full set.  Then, we also have an article about when it’s time to replace trailer tires.

Thank you for joining us for the read.  Have a Wonderful Day.


Notify of
Inline Feedbacks
View All Comments

We Found These For You . . .

A Unique Trailer Project
There is always something to learn when looking at someone’s DIY project.  This customer story about a unique trailer build is no exception.

Read The Article

Gantry Crane Failure Modes
In the debate about Steel or Aluminum for beams of trailer frames and gantry cranes, there is one big piece we hear less about.  An important part of the equation, for sure, is the property of Elasticity . . .…

Read The Article

4' x 8' - 3500# Torsion Axle Trailer

Fully Engineered Blueprints are just the start with these Torsion Axle Utility Trailer Plans.  With the deck a little larger than tradition, you can put true 4' x 8' cargo inside!  Up to 3500 lbs.

Air Ride Trailer Suspension
If you’re looking for something a little different in trailer suspension, one good approach is air.  It’s a little off the beaten path, but not too far, and there is a lot of support for doing it.  For a smooth…

Read The Article

6x16 Tandem Axle Trailer Plans

Build a great tandem axle, heavy duty utility trailer from these 6x14 trailer plans.  Blueprints are fully engineered for 12,000 lb. total capacity.  The trailer you build will be tough and ready to work.

Drill Fixture Zoom In
Oh, I need to drill a bunch of holes, all the same, in 8 parts.  What a pain!  And, I need to cut these other 5 pieces all to match.  What a hassle to measure, mark, and cut each one!…

Read The Article

6x10 Heavy Duty Trailer Plans

For all the jobs a utility trailer must do, these plans include so many options for both function and utility.  At 6+’ wide 10’ length, this design also includes an axle option for 6000 lbs or 7000 lbs.

Winch Drive Gantry Crane Leg Extender

Do you want an easier, faster, more controlled way to raise the top beam of your Gantry Crane?  We have it, with these winch driven leg extender plans that go with all the Gantry Cranes here at Mechanical Elements.

Drill Matching Bolt Holes
So many times we need to make matching holes to bolt something on.  You purchased something to mount on your trailer or your workbench or some other project, but now you need the exact

Read The Article

Just The Right Size Garage Crane

Get maximum height with a garage crane that still rolls through the door! Use it outdoors, then roll it right in. These Gantry Crane Plans have telescoping legs with options for the beam size and length.