Please see below pictures to know how to measure accurately.
This is also the way we use for our walk-in customers.

 

Neck

Where center of collar would be if you were wearing a shirt. To measure the neck open collar and place tape around neck where collar would rest. Take a loose measurement at this point for a comfortable fit. Just make sure you feel comfortable. Normally, it should be able to fit with two fingers (about 3/4 inch).

Measure the collar length from a finish shirt

If you measure from a finish shirt, you should measure from the middle of button hole to middle of button. You may also increase or decrease the finish shirt neck size based on your preference.

Measure from Middle of button hole to the button.



          
Half Shoulder and Sleeves

With arm straight and hand in a fist. Take two measurements, first from center of neck to the shoulder seam (just before shoulder drop) and measure from shoulder seam to the end of the shirt cuff with the cuff unbuttoned. Or if a good fitting shirt is not available, you may measure to the knuckle of little finger minus 1.5".

 

    

** 1+2 = Your Sleeve Length... Both Left and Right

Shoulder

Your shoulder size has been entered here based on double the (1) you measured earlier for sleeves.

Chest

Put tape around the fullest part of the chest (hands down and standing relaxed).

Waist

Put tape around the fullest part of the waist (against skin, not over pants). Tape should be snug with one finger between tape and body.

Hips

Put tape around the fullest part of the hips over pants). Tape should be snug with one finger between tape and body.

  Length

Measure in the back from base of the neck to an inch below hip line. It should hang at least six inches below the waist so that it stays tucked in when you move around. It should not be so long, however, it creates bulges in front of the trousers. You can also measure the shirt length from  point F to point G. (Point F is the highest point of the shoulder, isn't from the yoke.)

Shape of Shoulder  
Green Color: Square Shoulder
Red: Normal Shoulder
Blue: Slope Shoulder
Yellow: Very Slope Shoulde
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Back Length is measuring from the middle of the back.

Cuff

Measure the actual wrist size.
If you wear a medium size watch add a " to that wrist for heavier watches add "

Measure the cuff width from a finish shirt

If you measure from a finish shirt, you should measure from the the edge to edge.