How to Adjust Upper and Lower Thread Tension on a Sewing Machine: A Complete Guide for Perfect Stitches

Introduction:

Uneven stitches, thread bunching, or fabric puckering? The culprit is often thread tension. Whether you’re a beginner or a seasoned sewist, understanding how to adjust the upper and lower thread tension on your sewing machine is essential for clean, professional-looking seams.

In this guide, we’ll explain what thread tension is, how to recognize tension issues, and step-by-step instructions for adjusting both upper thread tension and bobbin (lower) tension—without the mystery.

What Is Thread Tension?

Thread tension controls how tightly the thread is pulled as stitches form. You have two main tension points:

Upper thread tension: Controlled by the tension dial on your machine.
Lower thread tension: Controlled by a small screw on the bobbin case.

When these are balanced, your stitches will look even on both sides of the fabric. If not, you’ll see looping, puckering, or inconsistent stitches.

Signs Your Thread Tension Needs Adjusting

Symptom	Likely Cause	Solution
Top thread is visible on the underside	Upper tension too loose	Increase upper tension
Bobbin thread is visible on the top	Upper tension too tight or bobbin tension too loose	Reduce upper tension or tighten bobbin tension
Puckered fabric	Tension too tight overall	Loosen upper and/or lower tension
Loops or nests of thread on underside	Upper tension too loose or threading issue	Re-thread and increase upper tension

Side-by-side fabric samples showing correct stitch tension and incorrect tension with visible looping and thread nests

How to Adjust Upper Thread Tension

Locate the tension dial (usually on the front or top of your machine).
Start with a medium setting (usually around 4 or 5).
Test on scrap fabric using the same material and thread as your project.
Adjust gradually:
- Turn the dial up (higher number) to increase tension.
- Turn the dial down (lower number) to decrease tension.
Stitch again and examine both sides of the fabric.

Tip: Always re-thread your upper thread before adjusting tension to rule out threading issues.

Close-up of a sewing machine’s upper thread tension dial with arrows showing direction to increase or decrease tension

How to Adjust Bobbin (Lower) Thread Tension

Note: Many modern machines rarely need bobbin tension changes. Only adjust if upper tension adjustments don’t fix the issue.

Remove the bobbin case.
Locate the tiny screw on the side.
Use a small screwdriver to:
- Turn right (clockwise) to tighten.
- Turn left (counterclockwise) to loosen.
Make small adjustments—just 1/8 of a turn at a time.
Reinsert the bobbin and test your stitches.

Alternative Test: Hold the bobbin case by the thread:

If it drops quickly, tension is too loose.
If it doesn’t budge, it’s too tight.
If it slowly lowers, it’s just right.

Photo of a bobbin case with a small screwdriver pointing to the tension adjustment screw

Balancing Both Tensions

The goal is for the upper and lower threads to meet in the middle of the fabric layers. Keep adjusting in small increments and test until the stitch is balanced.

Tip: Keep a tension log—note settings that work well for different fabric/thread types.

Cross-section diagram of fabric showing the upper and lower threads meeting at the middle layer for a balanced stitch

Conclusion: Take the Mystery Out of Tension

Thread tension doesn’t have to be intimidating. With a few simple tests and adjustments, you can fix most stitching problems quickly. Whether you're quilting, hemming, or sewing delicate fabrics, mastering tension means better results—and less frustration.