Shoulder width is measured across the back, from the bony tip of one shoulder to the bony tip of the other, with the tape held straight and the arms hanging relaxed. To find each tip, raise the arm sideways to horizontal: a small hollow appears at the top of the shoulder, and the bone in front of that hollow is the point. The same method, find a landmark on the skeleton and measure between landmarks, is what makes the other difficult measurements reliable: back waist length, bust height, arm length, crotch depth and waist to hip.
Why is shoulder width the measurement people get wrong most often?
Because both ends are soft, rounded places with no obvious edge, and a 2 cm (3/4 in) error moves the sleeve seam visibly. Measure too wide and the armhole seam slides down the arm, the sleeve cap collapses and folds appear at the top of the sleeve. Measure too narrow and the sleeve pulls across the shoulder every time you reach forward. Girths like the bust and hip forgive a centimeter, because ease absorbs it; the shoulder has almost no ease to absorb anything.
The second reason is posture. Most people stand up straighter when a tape comes near, which pulls the shoulder blades back and the shoulder points with them. Measure in the posture you live in, looking ahead, breathing normally.
How do you find the shoulder point?
- Stand in front of a mirror, or have a helper stand behind you.
- Lift one arm out to the side until it is level with the floor. Watch the top of the shoulder: a dimple appears where the arm bone meets the shoulder.
- The bony ridge directly in front of and above that dimple is the acromion, the end of the shoulder. Press it with a finger; it does not give.
- Lower the arm and keep the finger there. Mark the spot with a small sticker, a dot of eyeliner or chalk on a close-fitting T-shirt.
- Repeat on the other side, then measure across the back from mark to mark. The tape lies flat across the shoulder blades; it does not follow the curve of the neck.
If you are measuring alone, a well-fitting woven shirt is the best substitute: lay it flat, buttoned, and measure from the top of one sleeve seam to the other across the back yoke. Only use a shirt whose sleeve seam actually sits on your shoulder, not a dropped-shoulder style. The guide to measuring alone covers the mirror and the sticker tricks for the rest of the body.
Which other measurements are tricky, and how do you take them?
Each of these has a landmark, a route for the tape and a classic error.
| Measurement | Landmarks | Tape path | Classic error |
|---|---|---|---|
| Back waist length | Bump at the base of the neck; natural waist | Straight down the spine | Starting too high on the neck, adding 2 cm (3/4 in) |
| Front waist length | Shoulder at the neck; bust point; waist | Over the bust point, then straight down | Pulling the tape straight and skipping the bust |
| Bust height | Shoulder at the neck; bust point | Diagonal over the bust | Measuring without the bra you will wear |
| Bust point to bust point | The two bust points | Straight across | Letting the tape dip between them |
| Arm length | Shoulder point; elbow; wrist bone | Over a bent elbow | Measuring with the arm straight, 2 to 3 cm (3/4 to 1 1/4 in) short |
| Crotch depth | Waist at the side; chair seat | Straight down, seated | Measuring on a soft sofa |
| Waist to hip | Natural waist; fullest part of the hip | Down the side | Stopping at the hip bone instead of the fullest point |
How do you measure back waist length?
Tip your head forward: the most prominent bump at the base of the neck is the seventh cervical vertebra, and every back length starts there. Tie a length of narrow elastic around the natural waist, the crease that forms when you bend sideways, and let it settle. Measure from the bump straight down the spine to the lower edge of the elastic. This number sets where the waist seam of a dress falls; a bodice drafted 2 cm (3/4 in) too long sits in a roll of fabric above the skirt.
How do you measure bust height and the bust point?
Wear the bra you will wear with the garment, because the bust point moves with it. Bust height runs from the point where the shoulder meets the neck, the spot where a necklace chain rests, diagonally down to the bust point. Bust point to bust point is a straight line between the two points, tape flat, not pressed into the hollow between them. Both decide where darts end: a dart that stops 2.5 cm (1 in) short of the bust point looks right, one that points above or below it never does.
Front waist length uses the same start and goes over the bust point down to the waist elastic. Compare it with the back waist length: the front is normally longer by 2 to 5 cm (3/4 to 2 in); a bigger difference means a full bust and a bodice that will need the full bust adjustment.
How do you measure arm length?
Start at the shoulder point you marked earlier. Put a hand on your hip so the elbow is bent, and run the tape from the point, over the outside of the elbow, to the wrist bone on the little-finger side. A bent elbow adds the length the sleeve needs for movement; a straight arm gives a sleeve that rides up every time you bend. Measure the upper arm girth while you are there, around the fullest part with the arm relaxed, because a sleeve that fits in length and binds in the bicep is a common disappointment and a full bicep adjustment is easy to plan ahead.
How do you measure crotch depth?
Sit on a hard, flat chair with your feet on the floor. Place a ruler flat across your thigh at the side and measure from the lower edge of the waist elastic straight down to the ruler. That is the crotch depth, the vertical distance the trousers must cover from waist to seat, and it decides whether the rise is long enough to sit in. It is not the crotch length, which runs between the legs from front waist to back waist; crotch depth vs crotch length explains how the two work together.
How do you measure waist to hip?
Down the side of the body, from the waist elastic to the level of the fullest part of the hip and seat. Look in the mirror from the side to find the fullest point; on many people it is lower than the hip bone, between 18 and 24 cm (7 and 9 1/2 in) below the waist. Skirts and trousers reach their full width at this level, so measuring to the hip bone instead gives a pencil skirt that is tight 5 cm (2 in) lower than it should be.
Which habits make every measurement more reliable?
- Tie the waist elastic first and leave it on. Half of these measurements start or end at the waist.
- Mark the shoulder points and the base of the neck before measuring anything else.
- Take each number twice. If the two differ by more than 1 cm (3/8 in), take it a third time.
- Write the numbers on the body measurements list in the same order, with the date. Bodies change; a measurement sheet from two years ago is a guess.
- Keep a finger under the tape for girths; keep the tape flat and unstretched for lengths.
What checks the numbers once you have them?
Compare them with each other. Shoulder width is usually between a quarter and a third of the bust girth; front waist length is longer than back waist length; crotch depth sits between 24 and 30 cm (9 1/2 and 12 in) for most adults. A number far outside those ranges is more often a tape error than an unusual body. Sewly's measuring assistant does this check for you: it explains each measurement as you type it, compares the value with your height and the nearest size, and flags a number that looks wrong before the pattern is drafted.