Grade bikini bottoms means that the size of the bottom garment increases or decreases. The amount you grade by depends on the size chart you will use.
Sizing varies from brand to brand so it’s entirely up to you what measurements you decide to use.
For the purpose of this demonstration we will use the below example. You will see there is a difference of 2” between each size for the bust, waist and hip measurements.
These measurements go around the body. Height differences are not usually shown on size charts so for changes in length we will use standard increments.
When we grade bikini bottoms up or down we don’t simply increase or decrease everything by the same amount, we need to take into account that different parts of the body increase or decrease disproportionately to each other.
Below is an example of a bikini bottom that has been incorrectly graded up by two sizes vs an example that has been correctly graded.
In the incorrect version the small pattern piece has been scaled proportionately to create the medium and large sizes. This has caused a number of problems which becomes more visible the further we grade.
Note how the gusset width becomes wider when scaled up. This is not ideal – the gusset should stay the same width across all sizes.
Also note the difference in the shape of the leg curve. When graded correctly, more width is added toward the top of the leg providing more coverage as we go up the sizes without adding to areas that would be uncomfortable to the wearer (e.g. between the legs).
INCORRECT Vs. CORRECT: How do we grade bikini bottoms correctly?
There are basic rules we can follow that ensures we grade disproportionately (the same as the human body grows disproportionately) as we go up through the sizes.
And remember, the same applies when grading down. Simply follow the same methods but decrease instead of increasing. The first thing to think about is the overall increase to the garment.
Referring to our size chart above, we can see that we want to achieve a 2” increase around the body. Because our garment is symmetrical, we will split each pattern piece in half to apply the grade.
Let’s add 1/2” to either side seam on both the front and back pattern piece. This will add the required 2” total.
Remember that the gusset does not increase in width. We also need to grow the garment in length, although this doesn’t increase as much as it does around the body.
Your typical bottom will grow up by 1/4” and down by 1/4”. Note the lower hip point has been repositioned horizontally but does not move vertically – shown with the red hold line.