Emerald Diamond Lattice Mermaid Gown: Free Crochet Pattern

There is something almost magical about a mermaid silhouette. The way it hugs the body through the torso and hips, then flares dramatically at the hem, creates one of the most striking shapes in all of fashion. Now imagine that silhouette rendered in rich emerald green, wrapped in a delicate diamond lattice stitch that lets the light play through every open square like sunlight filtering through sea glass. That is exactly what this free crochet pattern will help you create — a showstopping Emerald Diamond Lattice Mermaid Gown that is entirely achievable, even if you consider yourself an intermediate crocheter.

This pattern has been designed with both beauty and wearability in mind. Whether you are making this gown for a photoshoot, a formal event, a costume, a beach cover-up over a bodysuit, or simply as a proud display of your fiber art skills, the instructions below will walk you through every step. The diamond lattice construction gives the gown an heirloom quality, while the mermaid shaping keeps it thoroughly modern and dramatic.

Let us get into everything you need to know.

Materials You Will Need

Before you cast on your first chain, gather your supplies. Having everything at hand before you begin makes the process far more enjoyable.

Yarn: You will need approximately 800 to 1,200 yards of yarn depending on your size. For the truest emerald effect, look for a medium weight (Category 4) yarn in a jewel-toned green. Yarns with a slight sheen — such as those with bamboo, silk, or modal blends — will catch the light beautifully and emphasize the lattice openwork. Solid colors work best for this pattern because the stitch detail is intricate enough on its own. Recommended options include Lion Brand Pound of Love in a green colorway, Paintbox Yarns Simply DK in Spearmint or Forest Green, or any smooth green yarn you love. For a full floor-length gown, budget on the higher end of that yardage.

Hook: A 4.0mm or 4.5mm crochet hook works well with most medium weight yarns. Adjust up or down a size if your gauge is off.

Notions: A yarn needle for weaving in ends, stitch markers, scissors, and a flexible measuring tape. If you plan to wear this gown directly against your skin, you will also want a bodysuit or slip to wear underneath, since the lattice is naturally open.

Optional: 6mm or 8mm elastic for the waistband, a few small buttons or a hidden zipper if you want a fitted back closure.

Gauge

Gauge matters more for this pattern than it does for many crochet projects because the fit of the mermaid silhouette depends on proper shaping. Take the time to make a gauge swatch before you begin.

Work a 6-inch by 6-inch swatch in the diamond lattice stitch pattern (see below) and block it gently with cool water and pins. Let it dry completely, then measure. You are aiming for approximately 16 stitches and 10 rows per 4 inches using a 4.5mm hook and medium weight yarn. If your gauge is tighter, go up a hook size. If it is looser, go down a size.

Understanding the Diamond Lattice Stitch

The heart of this gown is the diamond lattice stitch, a timeless openwork pattern that creates a series of diagonal mesh squares arranged in a diamond formation. It is worked with chains and double crochet clusters, and once you get the rhythm of it, it moves along quickly.

Here is the basic unit of the stitch:

Abbreviations used throughout:

• ch = chain
• sl st = slip stitch
• sc = single crochet
• dc = double crochet
• hdc = half double crochet
• sp = space
• rep = repeat
• sk = skip

Foundation Row: Chain a multiple of 6 plus 4. For a size small, chain 100. For a medium, chain 112. For a large, chain 124. Adjust as needed for your measurements (see sizing notes below).

Row 1 (Right Side): Dc in the 4th chain from hook. (Ch 2, sk 2 ch, dc in next ch) rep across, ending with dc in last ch. Turn.

Row 2: Ch 5 (counts as dc + ch 2), sk first dc, (dc in next dc, ch 2) rep across, dc in top of turning ch. Turn.

Row 3: Ch 3, dc in first ch-2 sp, (ch 2, dc in next dc, ch 2, dc in next dc) rep across, working last dc in 3rd ch of turning ch. Turn.

Row 4: Ch 5, dc in next dc, (ch 2, dc in next dc) rep across. Turn.

Repeat Rows 3 and 4 for the pattern. You will find that after just a few repetitions, the diamond shapes begin to emerge naturally from the mesh. The key is keeping your tension even throughout so that the diamonds align cleanly.

Sizing and Measurements

This pattern is written for sizes XS through XL, with notes for adjustments. Take your measurements carefully before beginning — bust, waist, hips, and desired length from the natural waist to the floor (or however long you want your gown).

The gown is worked in three main sections: the skirt (from hem to hip), the mermaid flare transition, and the bodice (from hip to bust). This structure makes it easy to customize length and fit.

Size Chart (finished measurements):

Extra Small — Bust 32 inches, Waist 24 inches, Hip 34 inches
Small — Bust 34 inches, Waist 26 inches, Hip 36 inches
Medium — Bust 36 inches, Waist 28 inches, Hip 38 inches
Large — Bust 38 inches, Waist 30 inches, Hip 40 inches
Extra Large — Bust 40–42 inches, Waist 32–34 inches, Hip 42–44 inches

For sizes above XL, add 12 foundation chains per size increment and adjust shaping rows accordingly.

Pattern Instructions

Part One: The Skirt

The skirt is worked flat in two panels (front and back) that are seamed at the sides, or you may work it in the round if you prefer a seamless construction. Working flat gives you more control over shaping. For a beginner to intermediate crocheter, flat construction is recommended.

Begin by working your foundation chain for your chosen size. Work the diamond lattice stitch pattern as described above, creating a rectangular panel approximately 22 to 28 inches wide and 30 to 36 inches long for a floor-length gown. This lower portion of the skirt does not require shaping — it is meant to be full and flowy at the hem. The natural drape of the open lattice stitch will give it beautiful movement.

Work two identical panels. When both panels are complete, seam them together along the sides using a slip stitch join or a mattress stitch, leaving approximately 10 to 12 inches open at the top of one seam for a side opening if desired.

Hem Finish: For the hem, work one round of single crochet along the bottom edge, then one round of reverse single crochet (also called crab stitch) for a neat, slightly textured border that will hold its shape well.

Part Two: The Mermaid Flare Transition

This is the section that transforms your gown from a simple skirt into a true mermaid silhouette. The flare is created through decrease rows that pull the fabric inward at the hips, then the body increases again as it moves up through the waist and bodice.

After completing the skirt panels, begin working the mermaid transition section. At the hip line, you will start working decrease rows to bring in the fabric. Work 4 to 6 rows of the lattice pattern, but instead of working into each mesh space across the full width, skip the outermost two mesh spaces on each side every other row. This effectively narrows the fabric to match your hip measurement.

The total width of the combined front and back panels at the hip should match your hip circumference measurement plus approximately 2 inches of ease. Once you have reached your hip measurement, stop decreasing and continue straight for 4 to 6 inches to create the close-fitting section that defines the classic mermaid shape.

Continue straight until the work reaches your natural waist. Here you may optionally add a simple waistband by working 3 to 4 rows of half double crochet in the round, inserting a length of elastic through the channel before closing it. This keeps everything in place beautifully, especially if you are wearing the gown without a bodysuit.

Part Three: The Bodice

The bodice is worked separately and seamed to the skirt, or you can continue working upward from the skirt in one piece. Continuing in one piece gives a cleaner finish but requires more careful measurement.

From the waist, continue the diamond lattice stitch pattern upward, increasing slightly at the bust by working an extra stitch into alternating mesh spaces every few rows. The exact number of increases depends on the difference between your waist and bust measurements. As a guide, for every inch of difference, add one additional repeat of the lattice unit spread across 2 to 3 rows.

Work the bodice until it reaches the height you want — typically just below the armhole. At this point you will shape the neckline and straps.

Neckline: For a sweetheart neckline, divide the work in half and work each half separately, curving the top edge by working short rows or by simply decreasing at the center front edge every row for 4 to 6 rows. For a straight bandeau-style neckline, simply bind off across the full width. For a halter neckline, work a long chain strap from each side of the front panel and seam them at the center back.

Back: Work the back panel to approximately 2 inches shorter than the front at the top to create a low open back. Use a few small hook-and-eye closures or a row of button loops along the back opening for a polished finish.

Putting It All Together

Once all sections are complete, lay the gown flat and check the overall shape before seaming. The silhouette should be clear: wide at the hem, narrowing sharply through the knee area, fitted at the hips and waist, then flaring slightly through the bust.

Seam the bodice to the skirt at the waist using a matching yarn and a mattress stitch. Weave in all ends carefully with a yarn needle, making sure every tail is secured on the wrong side so that nothing peeks through the open lattice on the right side.

Block the finished gown by soaking it in cool water, gently pressing out excess moisture in a towel (never wring), and laying it flat on a blocking mat. Pin the hem to the desired length and shape, and pin the lattice squares open to their full size so the diamond pattern is crisp and clear. Allow it to dry completely — this may take 24 hours depending on the yarn fiber. Blocking is not optional for this gown. It transforms the texture from slightly uneven to gloriously refined.

Color and Yarn Substitution Tips

Emerald green is the classic choice for this gown because it evokes the deep, mysterious color of the ocean and gives the whole piece the drama it deserves. But this pattern translates beautifully in many other colors. Deep sapphire blue creates an almost celestial effect. Dusty rose gives it a romantic, bridal quality. Black is timeless and gothic-glamorous. Ivory or champagne reads as vintage and elegant.

If you substitute yarn, stick to smooth, plied yarns rather than fuzzy or textured varieties. The lattice stitch requires clean, defined stitches to read properly. Mohair blends and boucle yarns will obscure the diamond pattern entirely. A slight sheen enhances the finished look significantly, so if your chosen color is available in both matte and lustre versions, opt for lustre.

Styling Your Emerald Diamond Lattice Mermaid Gown

The gown itself makes such a statement that you do not need to compete with it in terms of accessories. Keep jewelry minimal — a pair of delicate gold earrings, a thin chain necklace, or nothing at all. Let the stitch work be the star.

Footwear can range from strappy heeled sandals to embellished flip flops depending on the occasion. For a fantasy or costume look, bare feet with ankle cuffs or shell jewelry create a beautifully cohesive mermaid aesthetic.

For hair and makeup, soft waves work beautifully with the flowing quality of the gown. A braided updo that shows off the back of the bodice is equally stunning. If you are photographing the gown for your crochet portfolio or social media, natural light near water — a beach, a lake, a garden fountain — will make the emerald color sing.

Tips for Success

Work slowly through the mermaid transition section. This is the most technically demanding part of the pattern, and it is worth taking your time to count stitches carefully so that both the front and back panels shape identically.

Use stitch markers liberally, especially at the beginning and end of each row, so you always know where your turning chains are. In lattice patterns, it is surprisingly easy to lose your place.

If you are making this gown to wear, try it on periodically as you work the bodice section. Crochet fabric can look very different on a dress form or lying flat versus on an actual body, and catching a fit issue early is much easier than frogging a finished bodice.

Finally, do not skip blocking. It is tempting to rush to the finish line, especially after such a substantial project, but blocking is what separates a handmade item from a handcrafted heirloom. Those ten minutes of preparation followed by a day of patience will reward you with a gown that looks as though it came from a boutique window.

A Note on Wearability

Because this gown features open lattice work throughout, it is designed to be worn over a bodysuit, slip, or swimsuit. The open diamonds are part of the visual appeal — they are meant to reveal glimpses of whatever is beneath them, which creates beautiful contrast and depth. Choose your underlayer thoughtfully. A forest green or black underlayer keeps the attention on the crochet. A contrasting color like gold or white creates a bolder, more maximalist effect.

Final Thoughts

Crocheting a full-length gown is one of the most ambitious and rewarding projects you can take on as a fiber artist. The Emerald Diamond Lattice Mermaid Gown asks something of you — patience, attention to detail, and a willingness to take your time — and in return it gives you something extraordinary: a wearable piece of art that you made with your own hands, stitch by stitch.

Every diamond in that lattice represents a moment you chose to create something beautiful. When you put this gown on — or hand it to someone who will cherish it — that effort becomes visible in the most literal sense. The work is there, open and gleaming, for anyone to see.

Take your time. Enjoy the process. And do not forget to share your finished gown with the crochet community. Tag your projects, post your progress photos, and inspire someone else to pick up a hook and start their own.

Happy hooking.