Thread Calculator
Estimate how much thread a seam consumes from its length and the stitch type, and work out how many bobbins or spools that needs.
At a glance
- What you enter
- Seam length to be sewn, Stitch type, Passes over the same seam, Thread on one bobbin, Thread on one spool, Thread weight
- What you get
- Thread needed, Thread needed in metres, Bobbins to wind, Spools to have on hand, Approximate thread weight
- Formula shown
- Yes, every step, right below your results.
- Cost and privacy
- Free, no account needed, and nothing you type is stored.
See worked examples ↓ Read the FAQ ↓ Share this calculator ↓
Results are estimates for general information only, always verify with a professional or official source before acting on them.
How to use the Thread Calculator
- 1 Enter Seam length to be sewn (in), Measure the seam line, then add every extra pass over the same length, such as a topstitch or an edge finish.
- 2 Enter Stitch type, Each stitch class uses a different multiple of the seam length. An overlock uses several times what a straight stitch does.
- 3 Enter Passes over the same seam (passes), A sewn and serged and topstitched seam is three passes.
- 4 Enter Thread on one bobbin (yd), A domestic bobbin holds roughly 35 to 45 yd of 40 weight thread. A serger cone holds 1,000 yd or more.
- 5 Enter Thread on one spool (yd), A standard domestic spool is 100 to 150 yd. Industrial cones run 5,000 yd.
- 6 Enter Thread weight (wt), 40 weight is the standard all purpose sewing thread. Lower numbers mean thicker thread.
- 7 Press Calculate. You get Thread needed, Thread needed in metres, Bobbins to wind, Spools to have on hand, Approximate thread weight, and every intermediate step stays visible under "How is this calculated?"
- 8 Change one number at a time to see what moves the result, that is usually the most useful thing a calculator can tell you.
Worked examples
Real numbers run through this calculator. Open any example to load it into the form above and change it.
A dress with 10 feet of seaming
120 inches of seam length, sewn, serged and topstitched, so three passes on a straight stitch.
You enter
- Seam length to be sewn
- 120 in
- Stitch type
- 1
- Passes over the same seam
- 3
- Thread on one bobbin
- 40 yd
- Thread on one spool
- 110 yd
- Thread weight
- 40
You get
- Thread needed
- 25.00 yd
- Thread needed in metres
- 22.86 m
- Bobbins to wind
- 1
- Spools to have on hand
- 1
- Approximate thread weight
- 0.75 g
Three passes over the same 120 inches is 360 inches of seam, which is 900 inches of thread.
Serging a quilt backing
A 200 inch edge finished with a four thread overlock.
You enter
- Seam length to be sewn
- 200 in
- Stitch type
- 4
- Passes over the same seam
- 1
- Thread on one bobbin
- 40 yd
- Thread on one spool
- 110 yd
- Thread weight
- 40
You get
- Thread needed
- 105.56 yd
- Thread needed in metres
- 96.52 m
- Bobbins to wind
- 3
- Spools to have on hand
- 1
- Approximate thread weight
- 3.17 g
One pass at 19 times the length is about 106 yards, which is why a serger is fed from a cone measured in thousands of yards.
Guides that go with it
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