What do the weaving terms EPI and PPI mean? Learn how to calculate the correct sett (EPI) and picks per inch (PPI) for weaving yarns. Discover how to balance warp and weft density, choose the right sett for your fibre, and weave fabrics with the perfect drape and structure.
Getting the sett (EPI – ends per inch) and PPI (picks per inch) right is one of the most important parts of planning a weaving project. Together, these two measurements control how your fabric feels, drapes, and behaves after finishing.
This guide explains how to measure and adjust your sett and PPI for any yarn or weave structure — helping you create fabric that’s balanced, beautiful, and made to last.
What Are EPI and PPI?
This Blog post is written in Imperial measures (inches) for UK and American weavers. Weavers who work with the metric system find conversion is easy since 1in is equivalent to 2.5cm. For example, reeds used in the loom to define the Sett can be found described with EPI or Dents per 10cm (divide this latter number by 4 to get the equivalent EPI).
- Sett (EPI or EPCm):Â The number of warp ends (vertical threads) per inch, or centimetre.
- PPI (Picks Per Inch or PPCm):Â The number of weft threads (horizontal yarns) per inch or centimetre.
These two values determine fabric density:
- Higher numbers = tighter, firmer cloth
- Lower numbers = softer, looser weave
A balanced fabric usually has similar EPI and PPI, but varying them intentionally can produce interesting textures and effects.
Step 1: Start with the Yarn – Measure Wraps Per Inch (WPI)
Your yarn’s thickness provides the foundation for your sett estimate.
To measure Wraps Per Inch (WPI):
- Wrap the yarn evenly around a ruler (not too tight).
- Count the number of wraps in one inch.
- Use these formulas:
- Plain weave: WPI ÷ 2 = approximate EPI
- Twill weave: WPI ÷ 1.5 (or ÷ 1.25 for a looser structure)
Example:
A yarn with 24 wraps per inch gives:
- Plain weave: 12 EPI
- Twill: 16 EPI
This is your starting point, to be refined through sampling.
Step 2: Factor in Fibre and Finishing
Each fibre type interacts differently with weave density:
- Wool: Fulls and shrinks — start with a looser sett.
- Cotton: Stable, needs a closer sett for strength.
- Linen: Crisp and strong — weave tightly for structure.
- Silk: Drape and sheen improve with a moderate sett.
Also consider finishing:
- For washed or fulled fabrics, use a looser sett and PPI.
- For decorative pieces, a tighter structure adds clarity and definition.
Step 3: Use Charts as a Starting Guide
Yarn and weaving suppliers often publish sett charts suggesting EPI and PPI ranges for each yarn weight and weave type.
However, remember:
- Yarn twist, fibre blend, and tension can alter results.
- Your personal beat and loom setup will also affect PPI.
Charts are helpful guides, not rules — real results come from hands-on testing.
Step 4: Weave a Sample to Find the Right Balance
Sampling reveals the true character of your yarn.
- Warp at your chosen EPI.
- Weave several inches, changing your beat to vary PPI.
- Wash, dry, and measure your sample after finishing.
Then evaluate:
- Balanced weave: Warp and weft are equally visible.
- Soft drape: Slightly lower PPI (gentler beat).
- Firm structure: Higher PPI (tighter beat).
Sampling is the best investment of time you can make before committing to a full project.
Step 5: Observe and Adjust
If the warp looks crowded, reduce EPI slightly.
If the weft packs too tightly, ease your beat.
If the fabric feels loose or unstable, add density by increasing EPI or PPI.
Trust your eyes and fingers — weaving is as tactile as it is mathematical.
Step 6: Keep Notes for Future Projects
Record everything:
- Yarn details and WPI
- Chosen EPI and PPI
- Loom settings and weave structure
- Finishing process and shrinkage
Over time, your notes will become your personal weaving reference, helping you achieve consistency and accuracy in every future project.
Final Thoughts
Mastering sett EPIÂ and PPI gives you complete control over your woven fabric.
- Start with WPI to estimate sett.
- Adjust for fibre and weave type.
- Sample and refine until warp and weft interact beautifully.
By balancing these two simple numbers, you can produce fabric that meets your exact creative and functional goals — whether you’re weaving a fine scarf, a sturdy rug, or a crisp linen table runner.