Midnight Navy Diamond Lattice Mermaid Gown: Free Crochet Pattern
There is something quietly magical about sitting down with a skein of deep navy yarn and knowing that the stitches you make today will eventually become a gown. Not just any gown — a mermaid silhouette with geometric diamond lattice panels, structured at the hips and flowing at the hem, the kind of piece that makes people stop and ask, “Did you make that yourself?” When the answer is yes, and when you can point them to a free crochet pattern to try it themselves, that magic doubles.
This Midnight Navy Diamond Lattice Mermaid Gown is one of those patterns you will return to again and again. It works for formal occasions, styled photo shoots, cosplay events, and even wedding receptions when made in the right yarn. The deep midnight navy colorway gives it a timeless, sophisticated edge, while the diamond lattice texture adds visual interest without overwhelming the silhouette. The mermaid skirt flares elegantly below the knee, making it universally flattering across a range of body types.
Whether you are an experienced crocheter looking for your next wearable art project or an intermediate maker ready to push your skills further, this pattern has everything you need. Let’s walk through the materials, gauge, construction method, stitch glossary, and row-by-row instructions together.
What Makes This Gown Special
Before diving into the pattern itself, it helps to understand the design philosophy behind it. Most crochet gowns fall into two categories: lacy and open (beautiful but sometimes impractical) or dense and structured (warm but heavy). This pattern sits in a thoughtful middle ground.
The diamond lattice stitch creates a repeating geometric pattern that gives the fabric texture and visual depth without creating large open gaps. This means the gown has a semi-opaque quality — elegant and refined, not revealing. The structure allows the fabric to drape beautifully while still holding the mermaid shape at the hips and thighs before releasing into a graceful flare.
The midnight navy yarn color is intentional as well. Navy is a neutral that photographs stunningly in both daylight and artificial lighting. It pairs effortlessly with gold, silver, ivory, blush, and white accessories. It reads as formal but not funereal, bold but not loud.
The construction is worked in pieces — bodice front, bodice back, and skirt — and then seamed together. This approach gives you the most control over fit, which matters enormously in a form-fitting mermaid silhouette.
Materials You Will Need
Getting your materials right before you begin will save you time and frustration. Here is what this pattern calls for:
Yarn: Approximately 1,800 to 2,200 yards of DK weight (light worsted) yarn in midnight navy. Look for a smooth, slightly shiny yarn with good drape — a cotton-acrylic blend or a bamboo blend works wonderfully here. Pure cotton will give you the most breathable result, but it is heavier. A yarn with a slight sheen will enhance the evening-wear quality of the finished gown. Suggested options include Lion Brand Comfy Cotton Blend in Navy, Paintbox Yarns Simply DK in Sailor Blue, or any similar DK weight yarn with 50 to 60% natural fiber content.
Hook: A US size E/4 (3.5mm) crochet hook for the bodice and a US size F/5 (3.75mm) for the skirt panels. The slightly larger hook in the skirt helps the fabric drape more fluidly through the flare section.
Notions: Yarn needle for weaving in ends and seaming, stitch markers (at least 10), measuring tape, a full-length mirror for fit checks, and a sewing needle with matching thread if you choose to add a lining. Optional: 12 to 18 inches of invisible zipper or hook-and-eye closures for the back opening.
Gauge: With the E/4 hook and your chosen yarn, you should be hitting approximately 20 stitches and 22 rows to a 4-inch square in the diamond lattice stitch pattern. Gauge swatching is non-negotiable for a fitted garment like this one. A difference of even half a stitch per inch can translate to several inches of difference across the full width of the bodice, so please swatch and adjust your hook size as needed before casting on the full garment.
Sizing and Measurements
This pattern is written for sizes XS through 3XL. The diamond lattice mermaid gown is designed with approximately 1 to 2 inches of negative ease in the bodice and hip sections for that fitted mermaid look, and 6 to 10 inches of positive ease through the skirt flare.
Take the following measurements before you begin: full bust, underbust, natural waist, high hip (about 4 inches below the natural waist), full hip (about 9 inches below the natural waist), and the length from your underbust to the floor (or desired hemline). Write these down and keep them nearby as you work.
Here are the finished garment measurements for each size. Remember, these are the finished dimensions of the gown, not your body measurements. You want the finished bodice to be approximately 1 inch smaller than your actual measurements at bust and hip for proper fit.
XS fits a 30 to 32-inch bust and 33 to 35-inch hip. S fits a 33 to 35-inch bust and 36 to 38-inch hip. M fits a 36 to 38-inch bust and 39 to 41-inch hip. L fits a 39 to 41-inch bust and 42 to 44-inch hip. XL fits a 42 to 44-inch bust and 45 to 47-inch hip. 2XL fits a 45 to 47-inch bust and 48 to 50-inch hip. 3XL fits a 48 to 50-inch bust and 51 to 53-inch hip.
Stitch Glossary
Before you begin the pattern, familiarize yourself with the following stitches and abbreviations.
ch: chain
sl st: slip stitch
sc: single crochet
hdc: half double crochet
dc: double crochet
tr: treble crochet
sp: space
rep: repeat
RS: right side
WS: wrong side
sk: skip
Diamond Lattice Stitch (DLS): This is the signature stitch of this pattern. It creates a grid of raised diamonds against a background of tighter single crochet rows. Here is how it works over a foundation of any multiple of 4 stitches plus 2:
Row 1 (RS): Ch 1, sc in first st, ch 2, sk 2 sts, sc in next st, ch 2, sk 2 sts, sc in next st; rep from across, turn.
Row 2 (WS): Ch 1, sc in first st, 2 sc in ch-2 sp, sc in next sc; rep from across, turn.
Row 3 (RS): Ch 1, sc in first st, sk 1 st, dc in skipped st 2 rows below, sc in next st, ch 2, sk 2 sts, sc in next st; rep from to last 3 sts, dc in skipped st 2 rows below, sc in last st, turn.
Row 4 (WS): Repeat Row 2.
Row 5 (RS): Ch 1, sc in first st, ch 2, sk 2 sts, sc in next st, dc in skipped st 2 rows below, sc in next st; rep from across, ending ch 2, sk 2, sc in last st, turn.
Repeat Rows 2 through 5 for the pattern.
This stitch creates the signature interlocking diamond look that gives the gown its geometric, lattice-like texture.
Construction Overview
This gown is constructed in five main sections: the front bodice, the back bodice (worked in two halves to allow for the back opening), the hip panel (which connects bodice to skirt and creates the fitted mermaid silhouette), and the skirt front and back panels (which are worked together in the round from the hip panel downward).
The construction moves from top to bottom. You will begin at the bust line, shape the bodice with increases and decreases as needed, work the hip panel in a tighter gauge to maintain structure, and then release into the flared skirt section. Seaming is done with a slip stitch join on the wrong side for a clean, nearly invisible seam.
Pattern Instructions: Bodice Front
Using the E/4 hook, loosely chain the number of stitches corresponding to your size across the bust line. For size M, this is 90 chains.
Foundation row: Sc in second ch from hook and in each ch across. (89 sc) Turn.
Work in Diamond Lattice Stitch for 4 inches without shaping. This covers the upper bust and chest area.
Bust shaping: On the next RS row, work to the center 30 stitches and place markers. Work these center stitches in the established DLS pattern, but work the outer sections (the side panels, approximately 20 to 25 stitches on each side) in sc only. This creates a gentle visual separation that mimics princess seam lines and gives subtle shaping through the bust.
Continue working in pattern for another 3 to 4 inches through the full bust section. Then begin decreasing 1 stitch at each side edge every right side row, 3 times total, to shape the waist. This brings in the sides by about half an inch on each side, creating the curved waist effect that is crucial to the mermaid silhouette.
After the waist decreases, work even for 2 inches.
Hip shaping: Begin increasing 1 stitch at each side edge every right side row, 4 times total, to flare out through the hip. This should bring the width back out to or slightly beyond the original bust measurement. Work even for 2 more inches after the last increase.
Fasten off. Weave in ends.
Pattern Instructions: Back Bodice
Work the back bodice in two equal halves to create the center back opening. Each half should be half the width of the front bodice, minus one stitch for the center edge.
For size M, begin each back panel with a chain of 45 stitches.
Work Foundation row as for the front bodice, then proceed in Diamond Lattice Stitch following the same shaping instructions as the front. The center back edge on each half is worked in sc only (no DLS) for a clean, straight edge along the opening.
When both back panels are complete, seam them to the front bodice at the side edges using a slip stitch seam on the wrong side. You should now have a complete fitted bodice open at the top (the bustline) and center back, and open at the bottom (connecting to the skirt section).
Pattern Instructions: Hip Panel
The hip panel is the connective section between the bodice and the full skirt. Switch to the F/5 hook here. You will be working in the round, joining the front and back bodice pieces at the bottom edges and working downward.
Join yarn at one side seam with a sl st. Ch 1. Work sc around the entire bottom opening of the bodice, placing a stitch marker at each side seam. Join with sl st to first sc. (approximately 180 to 200 sc around for size M)
Work in DLS in the round for 6 rounds without shaping. This creates a snug hip panel that reinforces the mermaid silhouette before the skirt begins to flare.
Pattern Instructions: Skirt
The skirt is worked in the round from the hip panel downward. It begins narrow and fitted before dramatically flaring out below the knee, creating the signature mermaid shape.
Continue working in DLS in the round for approximately 12 to 14 inches without shaping. This is the thigh section of the skirt, which stays fitted.
Flare section: Begin working mermaid flare increases. On the next round, work the DLS pattern as established, but at each side marker (and two additional points spaced evenly around the circumference, so 4 increase points total), work an increase by placing 2 dc in the same stitch at the base of each diamond motif.
Continue working the flare increases every 4 rounds, 6 to 8 times total, until the skirt has opened to approximately double its original circumference at the hip panel. The final circumference of the hem for size M should be approximately 120 to 140 inches, which gives the gown a sweeping, dramatic mermaid flare.
Work even for 4 to 6 more rounds after the final increase round, then work one round of sc around the hemline for a clean finished edge. Fasten off.
Neckline and Back Opening Finishing
For the neckline, join yarn at the center front of the bustline and work one round of sc around the entire neckline edge. You can leave it as a simple sc edge for a clean finish, or work a second round in reverse sc (also called crab stitch) for a more decorative corded edge that holds the neckline’s shape beautifully.
For the back opening, work one row of sc along each back edge, then sew in your chosen closure. If using hook-and-eye closures, space them approximately 1.5 inches apart along the full length of the opening. If using an invisible zipper, hand baste it in place first, then secure it with whipstitch using matching sewing thread.
Styling Your Midnight Navy Diamond Lattice Mermaid Gown
The beauty of midnight navy is its incredible versatility as a base for styling. For a romantic evening look, pair the gown with gold statement earrings, strappy heeled sandals, and a simple updo. The geometric lattice pattern is the star of the show, so keep your jewelry relatively simple and let the texture speak.
For a more dramatic look — perfect for a styled photo shoot or cosplay event — consider adding a sheer navy or midnight blue capelet, arm cuffs in matching yarn, and dramatic eye makeup that echoes the angular quality of the diamond stitch.
If you are making this gown for a beach or destination wedding celebration, consider pairing it with metallic silver sandals, shell accessories, and loose, beachy waves in your hair. The mermaid silhouette and the name itself make this pairing feel entirely intentional and cohesive.
Tips for Success
Work your gauge swatch before anything else, and wash and dry it the same way you intend to care for the finished gown. This is especially important with yarns that contain cotton or bamboo, as they can relax significantly after washing.
Try on the bodice as you go. Because crochet fabric has some stretch, you will want to try the bodice against your body at the waist shaping stage and again at the hip shaping stage before committing to the measurements on paper.
Block the finished gown before adding closures. Wet blocking with mild soap will even out your tension, open up the diamond lattice motifs beautifully, and help the skirt hang with a more graceful drape.
If you find the skirt too heavy after blocking, consider switching to a bamboo or tencel-blend DK yarn, which offers excellent drape with significantly less weight than cotton.
Take your time with the seaming. The quality of the side seams and the join between the bodice and skirt panel will determine how polished the finished gown looks. A little extra time spent on neat, even seaming is always worth it.
Sharing Your Finished Gown
When you finish your Midnight Navy Diamond Lattice Mermaid Gown, share it with the crochet community. Tag your photos with the pattern name and post them to Ravelry, Instagram, or Pinterest. Your finished object photos inspire other makers to try the pattern, help others understand how the sizing works on different body types, and contribute to a broader culture of wearable crochet that celebrates craftsmanship and creativity in equal measure.
This gown is a project. It takes time, concentration, and care. But when you slip it on for the first time and see that midnight navy lattice catching the light, the structure hugging and then releasing at exactly the right points, the hem pooling or hovering just above the floor — you will know exactly why you started it.
Happy crocheting.
