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Curtain Fullness, Total Width & Drop Allowances

Calculate combined curtain width from fullness and compare half-height, four-inch and ten-inch drop allowances.

Formula & worked example
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Calculator inputs

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How to use this calculator

Enter the known values in the units shown. Results update as you type.
Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
Use the worked example to check the method. Reset restores the starting fields.

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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

For a 100 cm width at double fullness, total flat curtain width is 200 cm. A 200 cm vertical measurement plus the four-inch allowance gives a 210.16 cm drop.

Total flat width = measured width × fullness; drop = selected vertical measurement + allowance, or half the measurement for café mode

Worked example

Enter these known values and leave the other values blank.

Drop rule: Measured drop plus 4 inches
Combined fabric fullness: 2× gathered fullness
Vertical measurement for the selected rule: 200 cm
Width to cover before gathering: 100 cm

Drop including the selected allowance: 210.16 cm
Combined flat curtain width: 200 cm

Assumptions and limitations

The returned width is the combined flat width of all panels. Divide by the number of equal panels when planning individual panel widths.
Measure the vertical span appropriate to your desired endpoint. The selected rule adds exactly 4 inches (10.16 cm), adds 10 inches (25.4 cm), or halves the entered height. It cannot infer the floor position from window height alone.
These are explicit planning allowances. Confirm the actual rod position, curtain heading, clearance and desired pooling before buying or cutting. Sewing hems, shrinkage and pattern matching are not added.
Dimensions are positive. Fullness choices are two, two-and-a-half and three times the width to cover.

Common questions

Is the calculated width for each panel?

It is the total flat width across the panels. Two equal panels each use half that total.

Does the floor-length option measure my room?

No. You supply the relevant vertical measurement. The calculator only applies the selected allowance.

References

Bookify uses exactly 0.0254 meters per inch for the retained four-inch and ten-inch drop allowances.

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