How to Measure Wheel Bolt Pattern: Lug Count and Bolt Circle Diameter

A wheel bolt pattern has two numbers: the lug count and the bolt circle diameter. In the code 5x120, 5 is the number of studs or lug holes and 120 is the diameter, in millimeters, of the imaginary circle that passes through the center of every stud. This diameter is also called the pitch circle diameter (PCD).

How you measure the diameter depends on the lug count:

• Even lug count (4, 6 or 8 lugs): measure from the center of one stud to the center of the stud directly opposite it.
• Odd lug count (5 lugs): no stud sits directly opposite another, so you use a shortcut measurement or a simple multiplication.

The tire sidewall does not show the bolt pattern. It does show the rim diameter, which is a separate number. You need both, so the article starts with the sidewall.

What the Numbers on the Tire Sidewall Tell You, and What They Don't

The tire sidewall gives the tire's size, construction and performance ratings. It never gives the wheel bolt pattern. Take the common marking 225/45R17 91V as an example:

The size string mixes units. Width is in millimeters, aspect ratio is a percentage, and rim diameter is in inches. The load index and speed rating are codes, not dimensions.

The rim diameter of 17 inches tells you the wheel size. It tells you nothing about how the wheel bolts to the hub. Two 17-inch wheels can have completely different bolt patterns, such as 5x100 and 5x120. You can only find the bolt pattern by measuring the hub or wheel, or from the vehicle or wheel specifications.

How Width, Aspect Ratio and Rim Diameter Set Tire Height

You can calculate sidewall height, overall diameter and circumference from the three size numbers:

• Sidewall height (mm) = width × aspect ratio ÷ 100
• Overall diameter (mm) = rim diameter × 25.4 + 2 × sidewall height
• Circumference (mm) = overall diameter × π (about 3.1416)

For 225/45R17:

• The sidewall is 225 × 0.45 = 101.25 mm.
• The overall diameter is 431.8 + 202.5 = 634.3 mm, about 24.97 in.
• The circumference is about 1,992.7 mm.

Comparing Two Tire Sizes

Upsizing the wheel while keeping a similar overall diameter is called plus-sizing. Comparing 225/45R17 with 225/40R18 shows how it works:

• 225/40R18: the rim is 1 inch (25.4 mm) larger, but the shorter sidewall offsets most of it. The overall diameter rises only about 2.9 mm, roughly 0.5%.
• 245/40R18: the wider tire has a taller sidewall at the same aspect ratio. Its overall diameter is about 18.9 mm (about 3%) greater than 225/45R17, and it covers about 3% more distance per revolution.

Limits of Calculated Tire Geometry

These figures are calculated geometry, not actual measurements. A tire's real dimensions vary with the manufacturer, the rim width it is mounted on, inflation pressure and tread wear.

A matching or similar overall diameter also does not prove a tire and wheel will fit a vehicle. Fitment depends on things the tire sidewall does not show:

• bolt pattern
• center bore
• offset
• lug seat type and thread size
• brake and suspension clearance
• load requirements

How to Measure Wheel Bolt Pattern Size: The Basic Method

You can measure the bolt pattern on the vehicle's hub studs or on the wheel's lug holes. Each lug hole on the wheel corresponds to one stud on the hub, so both give the same result.

1. Count the lugs. Count the studs on the hub or the lug holes on the wheel. This is the first number in the pattern, such as the 5 in 5x120.
2. Find the center of each stud or hole. All bolt circle measurements are taken to stud centers, not stud edges. The 5-lug shortcut below is the only exception.
3. Measure using the method for your lug count. Use the 4-, 6- and 8-lug method or the 5-lug method described below.
4. Record the result in millimeters or inches. Convert if needed and compare it with standard bolt patterns.

Some wheels have the bolt pattern cast or stamped on the back of a spoke or near the mounting face. If you find such a marking, still confirm it with a measurement.

How to Measure Wheel Bolt Pattern: 4 Lug

To measure a 4-lug bolt pattern, measure from the center of one stud to the center of the stud diagonally opposite it. That distance is the bolt circle diameter.

On a 4x100 pattern, opposite stud centers are 100 mm apart. On a 4x4.5 pattern, they are 4.5 in (114.3 mm) apart.

Do not measure between two neighboring studs on a 4-lug wheel. That distance is shorter than the bolt circle. If you only have neighboring studs to work with, multiply the center-to-center distance by 1.414 to get the bolt circle diameter.

How to Measure Wheel Bolt Pattern: 5 Lug

A 5-lug bolt pattern has no directly opposite studs, so a straight center-to-center measurement across the hub will not give the bolt circle diameter. There are two practical methods.

Method 1: Back-of-Stud to Center Shortcut

1. Choose any stud as the starting stud.
2. Skip the stud next to it and go to one of the two studs farthest away.
3. Measure from the outer (far) edge of the starting stud to the center of the far stud.

This shortcut is an approximation. It works because, on common stud sizes, the extra half-stud width roughly makes up for the far studs not being directly opposite. It is usually close enough to tell apart patterns that differ by several millimeters. It is not precise enough to separate patterns that are only 1–2 mm apart.

Method 2: Adjacent Stud Measurement and Multiplication

1. Measure from the center of one stud to the center of the stud right next to it.
2. Multiply that distance by 1.701 to get the bolt circle diameter.

For a 5x120 pattern, adjacent stud centers are about 70.5 mm apart (70.5 × 1.701 ≈ 120). For a 5x100 pattern, adjacent stud centers are about 58.8 mm apart (58.8 × 1.701 ≈ 100).

If you measure center-to-center between two studs that are not neighbors, multiply by 1.051 instead.

How to Measure Wheel Bolt Pattern 5x100

A 5x100 bolt pattern has 5 lugs on a 100 mm bolt circle. You should get:

• about 100–101 mm with the back-of-stud shortcut
• about 58.8 mm center-to-center between neighboring studs

The closest inch pattern is 5x4 (5x101.6 mm). It is 1.6 mm larger, so the two are not the same pattern.

How to Measure Wheel Bolt Pattern 5x120

A 5x120 bolt pattern has 5 lugs on a 120 mm bolt circle. You should get:

• about 120 mm with the shortcut
• about 70.5 mm between neighboring stud centers

It is easily confused with 5x4.75, which converts to 5x120.65 mm. The 0.65 mm difference is too small to detect reliably with the shortcut or a tape measure. When a reading lands near 120 mm, confirm the exact pattern from the vehicle or wheel specifications.

How to Measure Wheel Bolt Pattern: 6 Lug and 8 Lug

Six-lug and 8-lug bolt patterns have even lug counts, so you measure them like a 4-lug pattern: from the center of one stud to the center of the stud directly opposite.

Common 8-lug bolt patterns include 8x6.5 (8x165.1 mm), 8x170 mm and 8x180 mm, often found on heavy-duty trucks and some trailers. The measured differences between these patterns are small enough that careful measurement matters:

• 8x165.1 and 8x170 differ by about 5 mm.
• 8x170 and 8x180 differ by 10 mm.

On a large 8-lug hub, measure several opposite pairs and compare them to confirm your reading.

Bolt Pattern Measuring Methods by Lug Count

How to Measure Wheel Bolt Pattern in mm and Inches

Bolt circle diameter can be written in millimeters (5x114.3) or inches (5x4.5). Both describe the same circle. To convert, multiply inches by 25.4 to get millimeters, or divide millimeters by 25.4 to get inches.

A metric pattern that looks close to a converted inch pattern is not automatically the same pattern. Examples are 5x100 versus 5x101.6, and 5x120 versus 5x120.65. Small bolt circle differences can stop the studs from aligning with the lug holes or place stress on the studs.

How to Measure Wheel Bolt Pattern With a Tape Measure

A tape measure can identify most bolt patterns if you read it carefully:

1. Use a tape with millimeter markings for metric patterns, or one with fine inch graduations (1/16 in or finer) for inch patterns.
2. Hold the tape flat across the face of the hub or wheel mounting surface, not angled over the studs.
3. Line the tape's zero, or a whole-number mark, up with the exact center of the first stud. Starting from a whole-number mark and subtracting avoids errors from a loose end hook.
4. Read the measurement at the center of the second stud, or at its far edge for the 5-lug shortcut.
5. Repeat on at least one other pair of studs and compare the readings.

A tape measure is reliable for telling apart patterns that differ by several millimeters, such as 5x100 and 5x114.3. It is not reliable for patterns within 1–2 mm of each other. For those, a caliper or a bolt pattern gauge gives a more dependable reading, and the vehicle or wheel specifications should confirm the result.

How to Measure Wheel Bolt Pattern on a Trailer

A trailer wheel bolt pattern is measured exactly like a car or truck pattern: count the lugs on the trailer hub, then measure the bolt circle diameter using the method for that lug count.

Trailer hubs commonly use 4, 5, 6 or 8 lugs, with patterns such as:

• 4x4 (4x101.6 mm)
• 5x4.5 (5x114.3 mm)
• 5x4.75 (5x120.65 mm)
• 6x5.5 (6x139.7 mm)
• 8x6.5 (8x165.1 mm)

On a 5-lug trailer hub, the shortcut can separate 5x4.5 from 5x4.75, since they differ by about 6 mm. Measure carefully all the same.

Trailer tire sidewalls often carry the ST prefix (Special Trailer) and a load range letter alongside the size. These markings describe the tire's intended use and load capacity. They do not describe the bolt pattern. A trailer wheel must match both the hub's bolt pattern and the trailer's load requirements, and the bolt pattern alone does not confirm the load requirement.

What a Matching Bolt Pattern Does and Doesn't Confirm

A matching bolt pattern confirms only that the lug count and bolt circle diameter of the wheel and hub agree. It does not confirm that the wheel will fit the vehicle. Several other measurements also have to match:

• center bore
• offset and backspacing
• lug nut or bolt seat type
• thread size
• brake caliper clearance
• load rating

Some wheels are drilled for two bolt patterns. These dual-drilled wheels have twice as many holes as the lug count, such as 10 holes for two different 5-lug patterns. Measure only the holes that belong to the pattern you are checking.

Read the tire sidewall for tire size and rim diameter, measure the hub or wheel for the bolt pattern, and treat each as one separate part of overall wheel fitment.