To create a bespoke Ovderbust corset for you, we'd need following measures:
Circuit A
Circuit B
Circuit C
Circuit D
Circuit E
Circuit F
Vertical measure B-C
Vertical measure C-D
Vertical measure D-E
Vertical measure E-F
Breast measure G (+ cup size you wear)
*Vertical measure while sitting

As you can see we need a lot of measures to create a perfect Overbust for you. That's why we made an instruction below with photos to make it easier!

Circuit A. It's our first measure, it goes exaclu over your breasts. You can put on a bra while taking measures to let the bra lift up your breasts a little (as the corset should lift up your breasts too). The A circuit is somewhere above the bra cups. My measure is 84 cm, so circuit A = 84 cm.

Circuit B. It's the widest breast circuit, more or less where nipples are. The measure tape shouldn't be too tight and too loose. Mine is 87 cm, so Circuit B = 87 cm. My cup size is B.
*You can take this measure with and without bra and give me both measures just in case.

Circuit C.  Underbust measure - while taking this measure you can wear a bra as well (not bralet!). Then a lower edge of your bra will be your underbust circuit measure. The measure tape shouldn't be too tight and too loose so take your measures carefully. Mine is about 75 cm, so circuit C = 75 cm.

Circuit D, Waist circuit. Your natural waist is somewhere between lover ribs and pelvic bones, usually 1-2" above a belly button. You can mark your waist with marker or tie a ribbon around it just to have a inmovable refference point and to measure yourself easier. You will need this during taking vertical measures. Mine is about 67 cm, so D circuit = 67cm.

Circuit E,  Pelvic bones circuit. The most important revverence point here are pelvic bones. They're not always sticks out so be careful while ascetrain them. For taking this measure I recommend to wear low rise pants and place it's upper edge around your pelvic bones. And then upper edge of the pants will be your E circuit, mine it's 84 cm, so E circuit = 84 cm

Circuit F, Hip circuit above groins. This measure is placed under your pelvis, somewhere about where groins starts and above pubic mound. Mine it's 93 cm, so F circuit = 93 cm.

Vertical measure B-C, measure between your nipples line and underbust line. Put the tip of your measure tape to the nipple line (where the B circuit goes) and check out the vertical measure to the underbust line (lower odge of the bra). Mine is 6 cm, so Vertical B-C = 6 cm.

Vertical measure C-D. Put the tip of your measure tape to the Underbust circuit (circuit A) and check out the vertical measure to the marked waist. Mine is 16 cm, so vertically C-D = 16 cm.

Vertical measure D-E. Put the tip of your measure tape to your marked waist and check out the vertical measure to the upper edge of the pants (E). Mine is 15 cm, so vertical D-E = 15 cm

Vertical measure E-F. Put the tip of the measure tape to the edge of your pants and theck out the vertical measure to the F circuit above the groins). Mine is 8 cm, so vertically E-F = 8 cm..

Breast measure G, Put the tip of your measure tape to the line where you measures A circuit, then check out the vertical measure through the whole breast to the underbust line, as the photo shows. Mine is 18 cm, with B cup, so Breast measure G = 18 cm.

*Extra vertical measure while sitting: sit down comfortly and put the tip of your measure tape to the marked waist, then check out the vertical measure to the area where the leg and groin starts. This measure shows us how long the corset's front can be to let you sit comfortly.

So correctly taken measures will look like (according to mine):
Circuit A = 84 cm
Circuit B = 87 cm
Circuit C = 75 cm
Circuit D = 67 cm
Circuit E = 84 cm
Circuit F = 93 cm
Vertical measure B-C = 6 cm
Vertical measure C-D = 16 cm
Vertical measure D-E = 15 cm
Vertical measure E-F = 8 cm
Breast measure G = 18 cm, with B cup
+Vertical measure while sitting X cm