Keep your arms at your sides. Measure from the fullest part of your upper arm for your bicep measurement. For the most accurate measurement, make sure the measuring tape is snug around your arm without squeezing.
To find your ideal sleeve length measurement, keep your arms at your sides. Measure along the side of your arm from the top of your shoulder and measure the length until the place you want the sleeve to end. This measurement will vary based on design preferences.