# Fractional Inch to Decimal and Millimetre Conversion Chart

> Source: https://netray.co/tools/fractional-inch-to-decimal-and-mm-chart-reference
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Every 1/32 inch from 1/32 to 1 inch with decimal inches and exact millimetres, searchable and exportable.

## Category

engineering-plm

## Audience

- Machinist
- Buyer
- Design engineer
- Quality engineer

## Tool

**Kind:** worksheet

**Mode:** reference

**Columns:**

#### Fraction (inch)

**Key:** fraction

**Type:** text

#### Thirty-seconds

**Key:** n32

**Type:** number

#### Decimal inch

**Key:** dec_in

**Type:** number

**Expr:** n32 / 32

**Format:** decimal

#### Millimetres

**Key:** mm

**Type:** number

**Expr:** n32 / 32 * 25.4

**Format:** decimal

**Rows:**

**Fraction:** 1/32

**N32:** 1

**Fraction:** 1/16

**N32:** 2

**Fraction:** 3/32

**N32:** 3

**Fraction:** 1/8

**N32:** 4

**Fraction:** 5/32

**N32:** 5

**Fraction:** 3/16

**N32:** 6

**Fraction:** 7/32

**N32:** 7

**Fraction:** 1/4

**N32:** 8

**Fraction:** 9/32

**N32:** 9

**Fraction:** 5/16

**N32:** 10

**Fraction:** 11/32

**N32:** 11

**Fraction:** 3/8

**N32:** 12

**Fraction:** 13/32

**N32:** 13

**Fraction:** 7/16

**N32:** 14

**Fraction:** 15/32

**N32:** 15

**Fraction:** 1/2

**N32:** 16

**Fraction:** 17/32

**N32:** 17

**Fraction:** 9/16

**N32:** 18

**Fraction:** 19/32

**N32:** 19

**Fraction:** 5/8

**N32:** 20

**Fraction:** 21/32

**N32:** 21

**Fraction:** 11/16

**N32:** 22

**Fraction:** 23/32

**N32:** 23

**Fraction:** 3/4

**N32:** 24

**Fraction:** 25/32

**N32:** 25

**Fraction:** 13/16

**N32:** 26

**Fraction:** 27/32

**N32:** 27

**Fraction:** 7/8

**N32:** 28

**Fraction:** 29/32

**N32:** 29

**Fraction:** 15/16

**N32:** 30

**Fraction:** 31/32

**N32:** 31

**Fraction:** 1

**N32:** 32

**Notes:** Millimetres use the exact definition 1 inch = 25.4 mm. Values are rounded for display only. For fractions in 64ths, double the numerator and denominator ratio: 1/64 inch is 0.015625 inch or 0.3969 mm.

## Content

**Intro:** Drawings, purchase orders and tooling catalogues still mix fractional inches, decimal inches and millimetres. This chart lists every 1/32 inch step with its decimal inch and exact millimetre value so you can check a size without opening a calculator.

**Sections:**

#### How to use the chart

**Body:** Type a fraction, a decimal or a millimetre value into the search box to find the nearest row. Use the decimal column when programming a CNC control or filling a decimal-inch drawing, and the millimetre column when ordering from a metric supplier. Export to Excel or CSV if you want to paste it into a tool crib list or an ERP unit-of-measure review. Remember that a stock size like 5/8 inch bar is a nominal size and the supplier tolerance still applies to the actual diameter.

#### The method behind the numbers

**Body:** Decimal inch equals the numerator divided by the denominator. Millimetres equal decimal inches multiplied by 25.4, which is exact since the 1959 international yard and pound agreement. Every value here is computed from the count of thirty-seconds, so there is no hand-typed rounding drift. The table therefore matches what a spreadsheet or a controller would compute, which matters when two departments each convert the same dimension.

**Bullets:**

- 1/32 inch = 0.03125 inch = 0.79375 mm
- 1/16 inch = 0.0625 inch = 1.5875 mm
- 1/8 inch = 0.125 inch = 3.175 mm
- 1/2 inch = 0.5 inch = 12.7 mm

#### Common mistakes

**Body:** The most frequent errors are rounding a converted size before applying a tolerance, treating a nominal fraction as a precision dimension, and converting a fraction like 5/16 to 0.31 instead of 0.3125 and then losing 0.0025 inch. Another is mixing fractional drill sizes with letter and number drill series, which are different tables. Keep full precision during calculation and round only the final stated dimension to the number of places the drawing tolerance supports.

**Cta:** If your item master stores sizes in more than one unit and the conversions drift between purchasing and the shop floor, we can help audit and automate the check inside your ERP.

**Faq:**

#### What is 5/8 inch in decimal and mm?

**Answer:** 5/8 inch is 0.625 inch, which is 15.875 mm. It is 20 thirty-seconds, so the chart shows it at row 20. Many metric suppliers will quote 16 mm as the nearest standard size, which is 0.125 mm larger.

#### Is the 25.4 factor exact?

**Answer:** Yes. One inch is defined as exactly 25.4 millimetres. Any rounding you see in the chart is a display choice only, not an approximation in the conversion factor itself.

#### Can I use this for drill sizes?

**Answer:** Only for fractional drills. Number drills (#1 to #80) and letter drills (A to Z) have their own decimal sizes that do not follow thirty-second steps, so use a drill size chart for those.

#### How do I get 64th inch values?

**Answer:** Divide the numerator by 64 for the decimal inch and multiply by 25.4 for millimetres. For example 5/64 inch is 0.078125 inch or 1.9844 mm. The 32nd values in this chart are every second 64th.

## Search terms

fraction to decimal inch chart, inch fraction to mm chart, 32nds to decimal chart, fractional inch to millimeter conversion, inch to mm conversion table, machinist decimal equivalent chart, fraction to decimal chart pdf, decimal inch chart excel

---
Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json