Measuring for the length:

If you have a curtain track:
measure from the bottom of your track to the place where you wish to see the bottom of your curtain.

If you have a curtain rod and rings:
measure from the bottom of the curtain ring to the place where you wish to see the bottom of your curtain

Measuring for the width:

Measure the window/door width, then multiply it by 1.5. You will get the total width you need for the curtains.

Consider whether you wish one curtain panel or a pair to cover the window. Having 2 curtain panels is more common for standard cases.

Example: the width 125 cm is for a not gathered panel. When fully gathered with S-fold tape the panel width becomes 84 cm.

For Thermal curtains to be effective, they must be installed properly.

Thermal curtains should be installed as close to the window frame as possible. They are most effective when they drop to the windowsill or floor.

Installing a cornice or valance above the drape further reduces the infiltration of air.