If you are going to put gutters around your house and you have some long sections, you are going to have to piece two sections of gutter together. Most gutters are sold in 10-foot sections. You don't need to have longer gutters professionally manufactured, as this can cost a lot of money. You can easily attach sections together to make each gutter the necessary length.
Measure how long you need the gutter to be. If you have a straight-run gable roof, measure from shingle to shingle, and then add 1/2 inch to each side. For outside corners, measure from corner to corner. If you have inside corners, subtract 5 inches. This will leave room for the inside box miter.
Add 4 more inches to the length you need. This is for the inside seam, and it will make the gutter stronger in that area.
Cut the second gutter with a hacksaw or tin snips. Check the measurements so that the total length of the first and second gutter when put together will equal the length you need, plus 4 inches.
Connect the two sections of gutter, overlapping the middle sections by 4 inches. Put the best-looking gutter edge or the gutter with the factory cut on the outside.
Apply gutter sealant where the two sections fit together. You need a tight seal so water doesn't leak through.
Secure the gutters with pop rivets at the sides of the joined sections. Never put rivets on the bottom because they could cause the gutter to leak. Allow the gutter sealant to dry according to the manufacturer's directions. Your gutter is now the correct length and ready to install.