Step 1: Things You'll Need to Get Sewing
-Thread (a color close to your pants)
-Ruler or tape measure
-A Pair of Pants (Pants that are too big or loose work better, so be careful with your adjustments if your pants are already snug. If you have a fuller 'bottom', start with larger pants would be best. These pants are about 1 size too big for me.)
Step 2: Cut Legs Off of Pants
-Use a pair of shorts that you already have and mark the length with chalk
-Stand in the mirror with your pants on inside out and mark the length you want the shorts part of your overalls to be with chalk.
After you have the desired length marked, use a ruler to mark one inch below your desired length and draw a line. This will be what is called seam allowance. Seam allowance gives you a little bit more fabric for your hem, otherwise your shorts will come out shorter than you planned.
Cut on the line you marked for seam allowance or a little below (It doesn't hurt to have too much seam allowance, but too little is a problem.)
Step 3: Hem the Bottom of Shorts
I recommend back stitching, which is when you overlap your stitches by going forward and backward so the stitches don't unravel when you wash your clothes. I backstitch at the beginning and end of each stitch.
Set the shorts aside. You will work with them again in a little while.
Step 4: Making the Top Part of the Overalls
To make the front part of the overalls:
On one of the pants legs, draw a trapezoid-like shape with proportions you choose (This means that your trapezoid shape is based on your body type and personal preference.) Use a ruler and chalk to draw an inch- thick border with seam allowance for your hem. You want the bottom of your trapezoid shape to match the width of the front of your shorts. This way, your overalls will look like ones that are sold in stores. Cut out and hem, like was done on the bottom of the shorts.
To make the back:
On the other pant leg, use chalk to draw a shape like the back of a racerback tee. It should be as long as the front, but more narrow. (You can use a racerback tee to get the top width right, the bottom width is up to you). Make sure to draw an inch border for your hem. Cut it out and hem.
Turn your shorts inside out. Pin the front piece upside down and on the wrong side to the front of the shorts. Use the middle seam in the top pieces to help you pin them properly. Do the same on the back of the shorts with the back piece. If you pinned horizontally, you will have to take them out as you sew. Placing your pin vertically allows the sewing machine to go over the pins. Sew around the entire waistline. Try to make the stitch as even as possible.
Step 5: Making Straps
After unpinning the straps, cut them about two inches below the line you marked. Make sure both straps are even. Fold the straps in half with the wrong sides facing outward and sew along the edge. You'll end up with a tube that you'll turn inside out. Iron them flat with the seam in the center of one side.
Pin the straps so they're even with back part of the overalls with the seam facing outward. Sew them to the back of your overalls and fold them upward and sew them again.
Step 6: Make a Pocket
Step 7: How to Make Matching Buttons
Step 8: Making the Buttonholes
On the loose end of the straps, cut off any excess about a 1/2 inch past where you'll attach your buttons. Fold the raw ends of the straps inward and sew them closed. Then draw a rectangle big enough for your buttons to snugly fit through. Make sure that the rectangles are even (you see what happens when they're not :P). Its better for the buttonholes to be a little too small for the button because they will get stretched over time.
Sew a zigzag stitch over the rectangles you drew. Go over each rectangle several times until you cannot see your markings. Use a seam ripper or sharp pair of scissors to cut out the center of the rectangles, making sure not to go cut the stitch.
Step 9: Attaching the Buttons
TIP: Use your ruler to measure the desired distance (from the end and the top of the overall top) to be sure the buttons are evenly spaced.