Ever stared at your envelope, wondering: Do I need extra postage for this? If you've ever slapped on an extra stamp “just in case”—you’re not alone. The good news? There's actually a lot you can mail with just one USPS Forever Stamp. So, here's how to answer the question:
Do I need extra postage?
Whether you're sending a birthday card, a love letter, or some important documents, knowing the USPS rules can save you stress (and stamps). Let’s break it all down, nice and easy:
💌 Rule #1: Your Envelope Must Be Rectangular
USPS machinable mail = rectangular only.
Square envelopes? Cute, but nope. USPS doesn’t consider a square a rectangle (even if geometry says otherwise). Sending a square envelope means you’ll need extra postage.
💡 Pro tip: Stick to standard, rectangular envelopes to stay in the one-stamp zone.
📐 Rule #2: Follow the Standard Letter Size Guidelines
To qualify for one Forever Stamp, your envelope must fit within these dimensions:
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Minimum: 5” long x 3.5” high
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Maximum: 11.5” long x 6.125” high
Anything smaller or larger? USPS calls that "non-machinable." Translation: extra postage.
📦 Rule #3: Keep It Slim — No Lumps or Bumps
The max thickness allowed is ¼ inch. So skip the bulky add-ins or chunky cards with raised embellishments.
Rigid or oddly shaped envelopes often need to be hand-canceled, which bumps you up into a higher price tier.
⚖️ Rule #4: Stay Under the USPS 1 Ounce Weight Limit
Forever Stamps cover up to 1 ounce. But how much is that, exactly?
Here’s a quick cheat sheet:
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💌 4 sheets of standard 8.5" x 11" copy paper = ~1 ounce
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🃏 One full suit from a deck of playing cards (like all the hearts) = just under 1 ounce
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📬 Most single greeting cards = safely under 1 ounce
If you're not sure? A cheap kitchen scale will become your best friend.
📭 Rule #5: Your Mail Has to Be Flexible
USPS mail goes through automated sorting machines. If your envelope is stiff, thick, or can’t bend? It’s officially non-machinable and will cost extra.
Things that make mail rigid:
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Cardboard inserts
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Photo prints taped to cardstock
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Overstuffed envelopes with stickers, bookmarks, etc.
✨ Rule #6: Fancy Envelopes = Possible Extra Postage
Planning to mail something extra beautiful?
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Wax seals
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Ribbon or twine
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Decorative clasps or layers
All of these can make your envelope non-machinable. That doesn’t mean you can’t use them—but you’ll likely need to:
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✅ Take it to the post office and ask for hand-canceling, OR
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✅ Place it inside a plain envelope for mailing
So, What Can You Mail with One Forever Stamp?
Here’s a quick list of what’s fair game for a single stamp:
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✅ Standard letters
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✅ Greeting cards (under 1 oz, no rigid bits)
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✅ Postcards (though they actually require less than a Forever Stamp!)
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✅ Checks, invoices, or other light documents
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✅ Pen pal mail, as long as it’s bendable and slim
Bottom Line: When In Doubt, Check the Weight
USPS Forever Stamps are pretty forgiving—but not limitless. Stick to standard size, flexible shape, and under 1 oz, and you’re golden.
Everything else? It’s not a big deal—you’ll just need a few extra cents of postage. Now go forth and mail with confidence! 📬✨
