Bell sleeves refers to a long sleeve that flares from the elbow to the wrist.  It is a very flattering and feminine sleeve style that has seen a comeback in the recent times. You can call it a part of the experimental exaggerated sleeve movement that has taken over the fashion trends. Today a number of flared sleeves are called Bell sleeves and here they are ; at least, some of them. 

Different types of Bell sleeves 

Flared one piece Bell sleeves

This is a one piece bell sleeve that flares at the hem, starting from the elbow . 

You can fold the sleeve fabric by half and mark.

The red line is the front armhole line. For drafting a sleeve checkout the post on drafting sleeves and for the armhole depth you can check out this post on armscye /armhole measurement

2 piece flared bell sleeves

This bell sleeve is added as an attachment to a regular 3/4 or half sleeve.To sew this bell sleeve draft and cut a regular sleeve and also cut a flared piece as in the picture below for the bell shape.

Attach to the regular sleeve

Circular Flounce Bell sleeves

Here the bell shaped piece is usually a circular piece of fabric with a lot of flare.

First draft and cut the regular sleeve. Sew the sleeve to the bodice.( or you can join the sleeve to the bodice after you have added the flounce) 

Take the measure of the circumference of the sleeve bottom edge. You will have to make a circle with a circular cut inside and this inner edge should fit the edge of the sleeve. How do you calculate the radius with which to mark the inner circle ?

For this take the circumference of the finished sleeve hem edge = say 15 inch.This is excluding the seam allowance. Take this as Y

Now with this measure it is easy to find the radius of the circle you have.

Radius = Circumference of the sleeve edge divided by 6.28

I got 2.38 inches. Mark a circle using this radius. This is A-B

Add 1/2 inch to the inside ( for seam allowance)

Now you have to mark the outer circle for cutting the sleeve piece.

Add 5 inch ( or the length of the flounce you want+ 1/2 inch seam allowance) to this radius you have calculated. This B-C

Mark the bigger circle outside with this radius

Cut out this donut shape.

You can also mark by folding your fabric piece twice (first by the center and then again once more) and then marking from the tip as in the picture below.

If you do not have enough fabric to make big single circles, join two fabric pieces to make the circle.

You will need two such circles for the two sleeves.

To sew the circle piece to the sleeve keep the circle piece and the sleeve right sides together and join the  two pieces together.

Trim and Clip along the seam allowance every 1/2 inch or so. You can then sew a zig zag stitch along the seam allowance to finish the edge.Make a baby hem along the outer edge.  

If you do not like the kind of flare a full circle has ( as can be seen from the photo below), you can reduce the flare by using the formula for making a half circle to fit the circumference of the sleeve hem edge. Check out the post on circle skirt calculator for more details and explanations.

Double layered Bell sleeves

This sleeve is made the same as the previous one – just one difference – you make two such circles  and inner one will be bigger than the other. Layer than and baste stitch in place before joining to the sleeve

High low Bell sleeves

In this case the flounce is cut so that the front portion has less length than the back -an  asymmetrical look which is interesting.

Frilly bell sleeves

Another type of bell sleeve can be attached as a gathered fabric to your regular sleeve. You can find more details on drafting this sleeve in the tutorial to sew a frilly sleeved top

You can find more such sleeves in this post on Frilly sleeves / Ruffle sleeves

Check out this post on sewing a top for directions to make such a sleeve.