It is helpful to know your room dimensions when looking to buy carpet, curtains, floors, tiles, sofa sets, sideboard, bed, dining table etc so you can plan your budget and choose the best quality you can afford.
Use a pencil, sketch out the existing layout & be sure to include the locations of all windows, doors, and cupboards.
Use a metal tape measure, to measure each wall, corner to corner. Label each wall A, B, C, D. It’s easier to hold the tape measure on the floor to measure. It’s also easier if you get someone to help you. Pick metric or imperial, use whichever you are most comfortable with.
Write down the sizes and locations (and heights if applicable) of each window, door, doorway , electrical and media outlets sockets, ceiling and wall fixtures including built-in bookcases, radiators, cupboards, alcoves, or wall projections, etc.
Measure and write down the ceiling height.
Now, measure each window from the floor to the bottom of the window, and again from the floor to the top of the window. Then measure the width of the window and write down all those measurements.
When you finish the first wall, total the measurement; it should match the first overall measurement. Continue this process around the room, and note the measurements on your drawing.
Double check this information:
Do you have plaster coving, and if so, how deep is it?
The location of all power outlets and light switches
The height and widths of windows and doors
The location of windows on each wall
The location of any wall lights, recessed and/or pendant ceiling lights
