What size flat pouch or single-serve sachet do I need?

How do I calculate usable interior space from outer flat pouch dimensions?

When you order 3-side-seal flat pouches or 4-side-seal sachets, the dimensions on your quote and dieline always refer to the outside trim edges of the flat packet. Around the perimeter sit heated crimp or flat-bar weld seams that fuse the inner sealant layers together to lock out air, humidity and liquid leaks. On small sachets under 4 inches wide, each side seal is typically 0.25 inches (¼ inch) wide; on larger 5 × 7 inch or 6 × 9 inch flat pouches, each side seal is 0.3125 to 0.375 inches (⅜ inch) wide. At the top of the pouch, you also need clearance for either a simple tear-open header or a reclosable press-to-close zipper track. A tear-open single-serve sachet needs about 0.625 to 0.75 inches at the top for the impulse seal and side V-cut tear notches. A resealable flat pouch needs 1.25 to 1.5 inches at the top to house the top weld, tear notches and zipper ribs. Always deduct those perimeter zones first before checking whether your folded sheet mask, trading card stack or powder scoop fits inside.

1. Usable Interior Width = Outer Width minus 0.5 in (small sachets) to 0.75 in (large flat pouches) for left and right side seals.
2. Usable Interior Height (tear-open sachet) = Outer Height minus 0.875 in (bottom seal + top impulse seal and tear notch).
3. Usable Interior Height (zipper flat pouch) = Outer Height minus 1.625 in (bottom seal + 1.375 in top zipper header).
4. Pillow-bulge allowance: add 0.5 × Item Thickness to both usable width and usable height so the film wraps around 3D contents.
5. Filling clearance: add at least 0.375 inches of extra mouth width so cards, wipes or funnels slide in without snagging.

What are the most common flat pouch and sachet sizes by product?

CubitPack builds custom flat pouches to any exact Width × Height in inches with zero die or plate charges, whether you need a miniature square wipe packet or a tall narrow electrolyte stick-style pouch. Across health supplements, cosmetics, specialty foods, seeds and collectibles, six proven sizes handle the vast majority of flat packaging projects. Use the benchmark table below to compare outer dimensions, usable interior cavity measurements, and typical dry or liquid fill capacities.

How does pillow bulge change flat pouch sizing for powders, gummies and masks?

On a stand up pouch, the W-folded bottom gusset unfolds to create front-to-back depth. On a flat pouch, all four edges are locked flat, so the only way the bag can hold volume is by bowing outward in the middle like a stuffed pillow. As the center of the packet puffs out to a thickness of $T$ inches, the front and back films travel along a curved arc rather than a straight line, which pulls the top, bottom and side edges inward. If you pack a 0.5 inch thick stack of beef jerky strips or a 0.5 inch mound of hydration powder inside a flat pouch without accounting for pillow bulge, the effective interior width and height shrink by roughly 0.25 to 0.375 inches, leaving your top impulse seal riding right over the product. Whenever your filled packet will puff out more than ¾ inch to 1 inch thick, either widen the flat pouch by 0.5 inches so the contents spread out into a flatter bed, or step up to custom stand up pouches with an expanding bottom gusset.

How do I size flat pouches for sheet masks, trading cards and seed packets?

Many flat pouch products are solid flat items rather than loose powders: folded non-woven facial sheet masks soaked in 25 ml of serum, standard 2.5 × 3.5 inch collectible trading cards, enamel lapel pins on backing cards, or inner glassine seed envelopes. For these rigid or semi-rigid inserts, corner clearance is the critical measurement. A standard 8-card foil booster pack of 2.5 × 3.5 inch trading cards is about 0.15 inches thick. Adding 0.5 inches for side seals plus 0.35 inches of sliding clearance gives a 3.35 to 3.5 inch outer width and a 4.75 to 5 inch outer height. For a folded hydrogel facial sheet mask measuring 3.5 × 4.75 inches in its plastic tray, a 5 × 7 inch foil-lined flat pouch leaves clean room around the tray so liquid serum never splashes into the top heat-seal jaw during filling.

How do I size flat pouches to fit USPS flat mailers and counter display boxes?

One of the biggest advantages of single-serve flat pouches is that they mail flat in referral envelopes and pack upright in checkout display cartons. Under USPS Domestic Mail Manual standards, a flat-rate envelope or machinable marketing mailer must stay uniform in thickness and under 0.75 inches thick. Sizing a 10-gram sample powder into a wider 3.5 × 5 inch or 4 × 6 inch flat pouch spreads the powder into a thin, flat layer under 0.25 inches thick instead of a fat round ball. If your flat pouches sell on retail shelves or cafe counters, coordinate your outer pouch width with custom display boxes. For example, twenty-four 3.5 × 5 inch sachets stand neatly in two rows inside a 7.5 × 6 × 5 inch pop-top counter display carton, giving your brand a tidy billboard right next to the cash register. When packing multi-day supplement kits, make the inner carton cavity 0.25 inches wider than your outer sachet width so customers can slide single packets out without catching the side heat seals on the paperboard.

What are the most common flat pouch and sachet sizing mistakes?

Avoid jammed filling funnels and leaky top seals by checking these five flat pouch sizing mistakes before you lock your dieline

1. Using outer Width × Height as interior cavity dimensions and forgetting to subtract 0.5 to 0.75 inches for the left and right side heat seals.
2. Forgetting to add half of the item's 3D thickness for pillow bulge, which leaves puffy powder or jerky packets too short to heat-seal.
3. Putting a bulky press-to-close zipper track on a tiny 3 inch or 3.5 inch tall single-serve sachet where V-cut tear notches work far better.
4. Leaving too little vertical headspace above wet facial sheet masks or liquid serums, allowing liquid to contaminate the top weld zone.
5. Making a mail-sample sachet too narrow and thick (over 0.75 inches puffed out) instead of widening the packet so it mails flat.

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