How to Calculate Elastic for a Cloth Diaper Pattern

Once you’ve resized your cloth diaper pattern, whether that’s by adding a wider crotch, a higher rise, and/or longer wings, the next step is figuring out how much elastic you need for the legs and waist. Getting the elastic length right is key to preventing leaks, avoiding gaps, and making sure the diaper is comfortable to wear.

In this tutorial, I’ll show you how to calculate elastic for cloth diaper patterns using a simple percentage method that works for both baby and adult sizes. I’ll also walk through real measurements from a resized pattern and explain how fabric choice can affect how your elastic behaves.

General Rule for Elastic

A good rule of thumb for baby, youth, and adult diapers is to cut your elastic to 65% of the measurement of the opening you’re elasticizing.

In other words:

Measurement × 0.65 = elastic length

If the wearer’s legs or waist are smaller or larger than average, you can adjust that percentage slightly up or down. For now, we’ll stick with 65% and walk through the calculations together.

Taking Measurements

To take measurements, simply use your measuring tape and measure between your elastic markings.

Front Waist Elastic

I personally like to add elastic to the front waistband because it helps prevent gaping. If you’re using hook-and-loop (Velcro) closures, this step is optional since the stiff hook and loop tape prevents the fabric from actually gathering.

The front waistband measurement on my resized pattern is 3 ⅛ inches.

Remember, patterns are cut on the fold, so I need to multiply by 2

• Leg Elastic
  • • 3 ⅛ × 2 = 6 ¼ inches
    • 6 ¼ x .65 = 4”

• Leg opening measurement: 13 ⅜ inches

• 13 ⅜ x .65 = 8.69 (we’ll round up to 8.75”)

Note that you can round down for a tighter fit or round up for a slightly looser one. If you need even more, you can multiply by .7 or .6. I don’t recommend multiplying by anything less than .55 because the elastic may not be able to stretch far enough.

Back Waist Elastic

• Back waist measurement: 5 ⅜ inches

• On the fold, so multiply by 2
• 5 ⅜ × 2 = 10 ¾ inches (or 10.75)
• 10.75 x .65 = 6.987 (rounding up to 7”)

A Note About Fabric & Elastic Behavior

How elastic performs depends heavily on the materials you’re using.

• Fold-over elastic on one layer of PUL will gather nicely and retract well.
• Elastic sewn into two layers of heavy fleece won’t retract as much.

Just remember, the heavier the fabric, the less the elastic (no matter what kind you use) will gather the fabric.