The finished bust measurement on a sewing pattern is larger than your own. That does not automatically mean you have selected the wrong size. The difference may be intentional space for movement and for the shape of the design.
Seamwork’s explanation of ease separates wearing ease, which allows movement, from design ease, which contributes to the silhouette. It also covers negative ease in suitable stretch garments. These ideas help explain why two patterns made for the same body can have very different finished measurements.
Subtract matching measurements
Consider an invented example: a body measurement of 96 cm and a finished garment circumference of 104 cm at the same location. The difference is 8 cm. That is the total difference around the body, not 8 cm at each side seam.
Make sure the figures describe the same place and use the same units. A flat width across a shirt is not directly comparable with a full body circumference. A measurement at the high bust is not interchangeable with one at the fullest part of the bust.
Compare the result with something you wear
Choose an existing garment with a similar fabric and intended shape. Measure it using the pattern maker’s method where possible. Note whether it feels comfortable when you sit, reach and move, rather than judging only its appearance on a hanger.
This comparison is a preference reference, not a substitute for fitting. A loose woven shirt and a close stretch top depend on different properties. Copying the numerical ease of one into the other can change the result substantially.
Read the fabric recommendations before sizing down a roomy design. Removing the space may also remove the intended drape. Conversely, increasing a close-fitting pattern can change shoulder and neckline relationships, not just the circumference you wanted to loosen.
Keep seam allowance separate from this calculation. Seam allowance is used to construct the seams; it is not extra wearing room waiting to be counted. If the distinction still feels unclear, mark the stitching line on a test piece and measure the finished shape.
A small fitting sample gives the numbers a physical meaning. Write down both the pattern size and the finished measurements you liked so the next project starts with evidence about your preferences.