Sheets can be a great material for making simple, no-sew slipcovers for upholstered sofas and armchairs, since they're large and easy to work with. You can buy designer sheets especially for making slipcovers, or you can find bargain sheets or even use old ones. Flat sheets, rather than fitted sheets, work best for covering furniture. However, if you want to use a sheet set, you can cut the elastic off of fitted sheets and use the material for covering seat cushions. Even leftover pillowcases can make great slipcovers for throw pillows.
Pick a flat sheet size that is large enough to easily drape over the entire chair or sofa from front to back and side to side. You'll need at least a full-size sheet for most chairs, and you may need two flat king sheets for a sofa or couch.
Buy about two dozen upholstery tacks, available at many home decor and fabric stores. Since some of the tacks will show, you may want to choose tacks that come in a colored or metallic finish, or even have heads shaped like flowers, for a decorative look.
Remove the seat cushions from the chair or sofa.
Drape the large flat sheet over the furniture so that it's completely covered. Depending on the size of the furniture, you may need to use one large sheet to cover the front, seat area and back of a sofa, and another sheet cut in half to cover the arms and sides.
Tuck the sheet into the seat area and any crevices, making sure there's still enough sheet left to cover the front and sides of the furniture.
Attach the sheet to the back of the seat area with upholstery tacks, if desired. Make sure to place the tacks as far back as possible.
Adjust the sheet over the arm areas, tucking it and folding it as needed to get a smooth fit. Hold the sheet in place with upholstery tacks along the undersides of the arms, and along the sides of the front of the arms if desired.
Adjust the sheet over the back of the chair or sofa so that the sheet lies as flat and smooth as possible against the furniture. Hold the sheet in place with upholstery tacks or safety pins.
Cut a piece of sheet fabric from a flat or fitted sheet that's large enough to wrap all the way around the seat cushion.
Lay the sheet fabric face down on the floor, and place the cushion upside down on top of it. Wrap the sheet fabric around the cushion like a package, and pin the edges together with safety pins. Cover any additional seat cushions the same way.
Replace the seat cushions, pin side down, on the chair or sofa. The seat cushions will help hold the slipcover in place.