Every car is different so you are going to need to measure your car parts for this tutorial.
Firstly measure the steering wheel width. You need to measure from the outside (green dots). To work out how long you need your fabric take the width (diameter) x3.14= circumference of wheel. Add 1″ to the circumference for joining the ends and cut to a width of 5.5-6″
My steering wheel cover piece is 5.5″x 46.5″ (cut 1). You will also need 2 lengths of 10mm elastic about 80% of your cover length
Next you can measure the seatbelt for the front seats and any adults are using. Using seat belt covers with child car seats is not safe. Measure around the whole belt blue dot to blue dot.
You need to add 2.5″ to this measurement this is 1/4″ for seam allowance, 1″ for overlap and extra because as you sew a padded item it covers less surface area. Length wise you need it around 7″. A good guide is 6.5″x 7″ (cut 2 from main fabric and one from wadding, piece of hook and loop 6.5″)
Last you need to measure the width of your headrest as this is where the bin will attach. If you want a hook over style rather than fasten on you should measure around the widest part of the cushion. My bin will be 9.5″x10″ when cut out this gives about 1/4″ seam allowance and 1.5″ to create a box base. Your strap needs to be about twice the width of headrest and around 2.5 ” wide. Mine is 2.5″ x 14″
STEERING WHEEL COVER
Fold the long edge under 3/8″ then another 1/2″ (top left & right) and sew into place
Thread your elastic through one end (bottom left)
When reach other side sew across the top to secure (bottom right)
Gauge how elasticated you want the cover and cut off excess, securing the end as you did before.
Repeat for other side then join the ends. using 0.5″ seam allowance.
I also added leather to the underside to keep it from slipping . If you wish to do this make it wide enough so when you sew your elastic channels you can sew this in place at same time.
This is mine complete
Place your fabric pattern sides together and lay wadding on top. (top left)
Sew along the sides leaving a gap for turning. (top right)
Clip corners and turn out the right way. Top stitch around the edge, closing up the gap (bottom left)
Lay one side of your hook & loop at right outer edge about 0.5cm in. Sew in place. Flip over keeping velcro from step 4 on your right and place opposite side onto left side of cover. Sew in place. (bottom right- shows opposite sides)
Place fabric for outer rides sides together and sew around 3 sides. Repeat for lining (leave top open. (left picture)
Match your side seam to bottom seam to create your box corner (see Yarn Cake Bag for more pictures of how to do this except your corner measurement should be 1.5″). (bottom right)
Sew across on both outer and lining corners and trim off. (top right is complete corner from outside)
Fold strap in half widthways , right sides together. and sew 1/4″ seam allowance sewing across one of the short edges, then turn out. (top left)
Place lining inside outer matching side seams, turn down the top edge about 0.5cm and pin. (top right)
Measure 1″ in from left side seam and place your unsewn strap edge between the layers. Top stitch lining and outer together securing the strap. (bottom left)
On sewn edge of strap sew on velcro or add snaps. 1″ in from other side seam place the other side of your velcro or snaps. (bottom right- completed in place)
If you are making a strap to go over the side without a fastening you need to repeat step 6 for other side and secure both ends of your strap between the layers.