How to Make a Cardboard Arch

Visit a building supply, furniture, or home supply store to get your cardboard. Ask an employee for big extra boxes. Most stores that sell furniture or large building supplies will have leftover packing boxes you can take for free. If you can find boxes that have packed doors, that would be a plus. Use a box cutter and a ruler to cut any cardboard down to the sizes needed.

Measure 1-foot in to the right and left sides of each of your 8 foot-by-8 foot cardboard sheets with your ruler. Mark these points with your marker or pen.

Place you ruler vertically on one of your marks and using your marker, trace a straight line. Continue this straight line about 6 feet. Repeat this step until all of your marks have become 6-foot lines.

Draw an upward curve from the left line to the right line on each sheet of cardboard with your pencil. It may take a few tries to get this curve to look even. When you are satisfied, trace over your line with marker. You will now have drawn the inward curve of your arch.

Round the top left and right corners into an arch using a pencil first, and then tracing over the final lines with your marker on each sheet of cardboard. You should now have the outlines of 2 arches you will be cutting out.

Using your scissors or a box cutter, cut along the lines you have drawn with your marker. Secure one 48-inch dowel rod onto the back of each leg of the arches with your clear duct tape. Secure one 12-inch dowel rod on either side of the top of each arch. The rods should cover most of the length of the arch.This will keep the cardboard from bending.

Decorate your arches and your other cardboard pieces to your liking by applying paint, glitter, and/or ribbons. If you want balloons on your arch, wait to apply these until the end of your project. Allow ample time for the paint to dry.

Cut 2 of your 1 foot-by-1 foot pieces of cardboard in half diagonally, creating 4 triangle pieces. Tape 1 triangle piece to the center base of each leg of your arches at a 90 degree angle. These will help support your arches when standing up.

Line up your arches. Attach the feet of your arches to the 2 foot-by-1 foot cardboard pieces. The feet should fit snugly onto the cardboard pieces.

Stand up your arch carefully. You may need to lean it against a wall. You can now evenly secure your 9 1 foot-by1 foot cardboard pieces between your arches, firmly attaching the two pieces together. The best way to do this is to tape one piece to each arch at the top while standing on a chair or stool, and then evenly taping the remaining 4 pieces to each arch down the left and right side.

Tape the tied ends of balloons along your arch if you please. Your arch is now complete, standing freely.