Understanding Sewing Machine Needle Sizes and Thread Weights

Apr 28, 2025 by Debbie NC Stitches

It happens to all of us. You need to find a sewing machine needle for your latest project. Selecting the correct sewing machine needle and matching thread weight can be confusing for beginners and even experienced crafters. When you are shopping online or visiting your favorite fabric store, finding the correct sewing machine needles and thread weights can be overwhelming. With so many choices, how do you know which to purchase?

To make matters worse, the naming conventions used for threads and needles do not make sense. The lower the needle size, the higher the corresponding thread weight. So a size 70 needle is paired with a 100-weight thread, which is a very fine thread.

This quick reference table should help when shopping for your next project.

70/10 needle pairs with a 100-weight thread (a very fine thread). A thinner thread is recommended when you do not want the stitches to show.
80/12 needle goes with a 50-weight thread – 50-weight thread is the most popular general-purpose thread, which is readily available in many colors.
90/14 needle pairs with a 40-weight thread – 40-weight thread is classified as a medium-weight thread and can be used with most cotton fabric.
100/16 needle goes with 30-weight thread – 30-weight thread is a heavier thread. I use 30-weight thread to add accents in my landscape quilts.

What the Numbers Mean

Thread weight is a defined measurement. A thread is labeled 40 wt when 40 kilometers of that thread weighs 1 kilogram. 30 weight thread is heavier because it takes only 30 kilometers of thread to weigh 1 kilogram. A lower thread weight number indicates a thicker thread.

Needle size consists of two numbers. The first number is the needle shaft diameter (in millimeters multiplied by 100). A standard “80” needle is .80mm in diameter. The larger the needle size, the thicker the shaft. (The second number is the US needle size.)

Why coordinate needle sizes with the thread weight?
Needles are not one-size-fits-all. The friction of pulling the thread through a too-tight eye can cause the thread to break. Mismatched sizes can cause frustration.

Tip: When in doubt, try going up a needle size.

Hopefully, this will help you with your next fabric/notions shopping trip.