Bag Closing Needle Size Calculator
Pick the bag closing thread you run and get the needle range published for it, or start from the needle already in the machine and see which threads it will take.
What this calculator does
It pairs a bag closing thread with the needle that runs it, in both directions: give it a ticket and it returns the published needle range, or give it the needle already in your machine and it lists every thread we make that is specified for it. Sizes are metric, Nm, where the number is the blade diameter in hundredths of a millimetre — Nm 150 is a 1.50 mm blade.
Every range comes straight from the Recommended Needles column of the specification tables on our spun polyester bag closing thread and polypropylene bag closing thread product pages.
How to use it
Choose My thread and pick your ticket to get its needle range, breaking strength and Tex. Choose My needle size and type or tap an Nm value to see every bag closing thread published for that needle, grouped by range.
Frequently asked questions
What does Nm mean on a sewing needle?
Nm is the metric needle number, and it is the blade diameter in hundredths of a millimetre. An Nm 150 needle has a 1.50 mm blade, an Nm 200 has a 2.00 mm blade. It is the sizing system used throughout our specification tables.
What happens if the needle is too small for the thread?
The thread is forced through an eye and a hole that are too tight for it. Friction and needle heat rise, the thread frays and breaks, and you lose production time to rethreading. On coarse woven PP the fluff also builds up inside the machine.
What happens if the needle is too large?
You punch a bigger hole than the thread fills. On woven PP and HDPE that means a looser seam that can leak fine product, and on laminated bags it can start a tear at the perforation line. Oversizing is not the safe direction it appears to be.
Why is a range given rather than one needle size?
Because the right needle within that band depends on the fabric, not only the thread. A heavy laminated FIBC panel and a light feed sack take the same thread differently. Start in the middle of the range and move within it based on how the seam and the machine behave.
Does polypropylene need a different needle from spun polyester?
Usually a heavier one at the same seam strength. Polypropylene reaches a given breaking strength at a higher Tex than spun polyester does, and a thicker thread needs a bigger blade. Our Tkt 20 spun polyester runs at Nm 130–160, while the polypropylene at the same strength is specified at Nm 160–200. Check with the equivalent finder before you change over.
Related calculators
- Sewing Thread Count Converter Ne, Tex, dtex, denier, metres per kg and yards per lb, in both directions and ply-aware.
- Bags Per Cone Calculator for Bag Closing Thread How many bags one cone will close, and the cones a run of 10,000, 1 lakh or 5 lakh bags needs.
- Monthly Bag Closing Thread Requirement Calculator Bags per day into cones per month, with how long a single cone lasts on your line.
- Spun Polyester to Polypropylene Thread Converter The equivalent bag closing thread in the other range, either direction, matched on strength or thickness.
Machine not behaving?
Tell us the machine, the fabric and the bag and we will work out the needle and thread pairing with you rather than leave you to trial it on the line. Talk to our technical team.