Sewing patterns, especially swimsuits) are a starting point, and to achieve the best personal fit, you may want to make some pattern adjustments.
Before cutting into your chosen fabric, it is worth investing a little time in creating a test fit first. This helps you see whether any personal adjustments are needed. If you do need to make corrections, you can transfer them to your pattern pieces so you can cut your final fabric with confidence.
The photos below show the pattern piece for Back Bottom of the Tropical Twist Swimsuit Sewing Pattern. When making the full swimsuit, it is a good idea to cut the entire suit from a different fabric first and baste the sleeves to the front and back. Also baste the side seams, and leave the crotch area open so you can try it on. Once the swimsuit is on, you can clip the crotch closed, evaluate the fit, and make any necessary adjustments.
Try on the lining bottoms or swimsuit with the wrong side facing out. The intended fit, without elastic, should gently hug your curves. It should not feel tight or overly loose.
You may need a full bum adjustment on a swimsuit sewing pattern when the back of the swimsuit feels too tight, pulls, rides up, or cuts into your bottom, even though the rest of the suit fits well.
Here are some signs that a full bum adjustment is needed:
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Wedgies or riding up at the back
The swimsuit doesn't stay in place over your bum and keeps shifting upward. -
Horizontal pull lines across the bum
Wrinkles or drag lines form from side seam to side seam across the fullest part of the bottom. -
Back seam curves into your bum uncomfortably
It feels like the suit is "disappearing" into your body in the back. -
The front fits fine but the back feels tight
The front crotch and waist seem okay, but the back feels stretched or skimpy. -
Your full hip or bottom measurement puts you in a bigger size than your waist
If you're grading sizes and your hip or bottom area is proportionally larger, you might need extra length or width at the back rise.
A full bum adjustment typically adds length and room to the back rise and the curve of the seat, allowing the swimsuit to cover your bum more fully without distortion, pulling, or riding up.
It helps maintain:
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Better coverage
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Improved comfort
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A more flattering silhouette
Full Bum/ Extra Coverage Adjustment
Step-by-Step:
Put on your Fit Version
Put on your Fit Version and determine how much extra room you need/want. Usually 0.5" to 1" (1.25 to 2.5 cm) is enough.
Draw a horizontal line
On the back pattern piece, draw a horizontal line across the fullest part of the bum (usually around the bottom curve of the cheek). This should be perpendicular to the grainline or center back seam.
Cut along the line
Cut along the horizontal line from the side seam, stopping just before the center back seam. You’re leaving hinges so the pieces stay connected.
Spread the pattern
Gently spread the lower section downward and slightly outward to add length and width to the bum area. Add about 0.5" to 1" (1.25 to 2.5 cm) depending on how much extra room you need. Make sure the crotch line still flows smoothly.
Fill in the gap
Tape the spread pieces down onto extra paper and redraw the outer lines to smooth out any jagged edges. Blend the side and center back seams.
Check your crotch seam length
You might need to slightly adjust the front piece too, so the crotch seams match in length again.
That’s it! This gives your swimsuit extra volume and comfort in the back.
