Use a soft measuring tape. Stand naturally, relax your arms at your sides, and measure over light clothing. Keep the tape level and snug but not tight.
Chest / Bust
Wrap the tape around the fullest part of your chest or bust, under the arms. Ensure the tape is level all the way around and breathe normally while measuring.
Natural Waist
Measure around the narrowest point of your torso (usually above the belly button). Keep the tape snug but comfortable — you should be able to slide one finger under the tape.
Hips / Seat
Measure around the widest part of your hips/seat. Stand with your feet together and keep the tape parallel to the floor for an accurate reading.
Sleeve Length
Measure from the shoulder point (where a shoulder seam would sit) down to the wrist bone with your arm relaxed. Measure along the outer arm for best accuracy.
Shoulder Width (optional)
Measure straight across the back from shoulder point to shoulder point. This helps when you want a precise fit across the upper back and sleeve head.