If your bust cup size is larger than the cup size used to draft a pattern, you may need to do a full bust adjustment. Here’s how to calculate the size of your FBA.
The average sewing pattern is drafted using a B cup, but the average woman wears a D or DD bra cup. That’s why here at Cashmerette, our patterns include three cup sizes for you to choose from (C/D, E/F, G/H) which add up to a better bust fit right out of the gate!
If you’re larger than an H cup, or if you’re using a pattern that wasn’t drafted for your cup size, you may need to do a full bust adjustment. In this tutorial, we’ll show you how to calculate the size of your FBA.
In order to calculate your FBA, you’ll first need to measure your high bust and full bust. Here’s how to take these measurements.
Got your measurements? Okay, let’s get started.
How to Calculate the Size of Your Full Bust Adjustment (FBA)
1. Pick your base size by comparing your high bust measurement to the high bust measurement line in the Body Measurements Chart.
- If your high bust is between sizes, go to the next size up.
- If your pattern does not have a high bust measurement line, you can calculate it. If the pattern is drafted for a sewing B cup, then subtract 2″ (5cm) from the full bust measurement to find the corresponding high bust measurement. If it’s drafted for a sewing C cup, subtract 3″ (7.6cm), for a sewing D cup subtract 4″ (10.2cm) and so on. Note that many patterns do not specify their cup size, but the default tends to be a B cup.
2. Compare your full bust measurement to the corresponding full bust measurement(s) for the base size selected in step 2. If the pattern has multiple cup sizes like Cashmerette, you will have several options.
- If there is a full bust size that matches your measurements in the same base size, that’s the size to use, no Full Bust Adjustment required!
- If your full bust measurement is larger than the largest full bust line in the chart, you will need to do a Full Bust Adjustment.
3. Calculate the difference between the largest available full bust size available in your base size, and your actual full bust size.
- This is the total amount you are going to add in your FBA.
4. Divide this number by 2.
- This is how much of an adjustment you’re going to make to your bodice piece (because the pattern piece is based on half your body).
Example of How to Calculate an FBA in Patterns With a High Bust Measurement Line
Let’s look at how to calculate an FBA if your high bust is 45″ and your full bust is 52″, and the pattern has a high bust measurement line in the chart, like Cashmerette.
1. Pick your base size by comparing your high bust measurement to the high bust measurement line in the Body Measurements Chart.
- Looking at the Cashmerette Body Measurement Chart below, we can see that 45″ is a size 20. This is now your base size.
2. Compare your full bust measurement to the corresponding full bust measurement(s) for the base size selected in step 2.
- Looking down the size 20 to the full bust lines, we can see the largest cup available is the G/H with a 50″ measurement. However, your measurement is 52″, so that means you need a full bust adjustment.
3. Calculate the difference between the largest available full bust size available in your base size, and your actual full bust size.
- The difference between your bust (52″) and the largest cup size full bust (50″) is 2″ total.
4. Divide this number by 2.
- 2″ divided by 2 is 1″ – so you will do a 1″ full adjustment on the bodice pattern piece.
Example of How to Calculate an FBA in Patterns Without a High Bust Measurement Line
Let’s look at how to calculate an FBA if your high bust is 38″ and your full bust is 43″, and the pattern does not have a high bust measurement line in the chart.
1. Pick your base size by comparing your high bust measurement to the high bust measurement line in the Body Measurements Chart.
- As this brand does not provide high bust sizing, you need to create your own line. This brand says they draft for a sewing C cup*, so to calculate the high bust measurement, you subtract 3″ from the full bust (which is simply labeled as “bust”). In the chart below, that has been added for a few sizes.
- As your high bust of 38″ is between sizes, you round up, so your base size is the 14.
*As noted above, many sewing brands do not specify, in which case, assume a B cup.
2. Compare your full bust measurement to the corresponding full bust measurement(s) for the base size selected in step 2.
- Looking down the size 14 to the full bust line, we can see it is 42″. However, your measurement is 43″, so that means you need a full bust adjustment.
3. Calculate the difference between the largest available full bust size available in your base size, and your actual full bust size.
- The difference between your bust (43″) and the largest cup size full bust (42″) is 1″ total.
4. Divide this number by 2.
- 1″ divided by 2 is 0.5″ – so you will do a 0.5″ full adjustment on the bodice pattern piece.
What to Do Next
So now you know how to calculate your FBA, you can move on to do the adjustment! We always recommend tracing your original pattern pieces prior to starting any adjustment, in case you need to refer back to the original piece at any point down the road. It’s also a great idea to make a fitting muslin first to check whether your FBA had its intended effects, before you cut into your precious final fabric!
Note, dartless knit FBAs are calculated slightly differently. Learn more about them here.
Absolutely wonder information on the FBA! Thank you so much for this.
I use a different method, by tissue fitting the pattern (similar to the Palmer-Plesch method and Pink Chalk Studio) and checking where my centre front (CF) is on the pattern, compared to the CF on my body that difference (say, 2.5 cm) is the amount I need to do a full bust adjustment.
Hi I am a G cup. That is why I always need to do a FBA