What this calculator works out

This calculator takes the height of the fitting above the floor, subtracts the clearance you want at the bottom, and applies any adjustment for the heading, giving a finished curtain drop.

Drop is measured from the point the curtain hangs from, which depends on the heading type — and getting that starting point wrong is the most common reason curtains arrive the wrong length.

Enter your details

Fitting height above floor (cm)

Floor clearance (cm)

Header adjustment (cm)

Your result will appear here.

Before you measure

The three figures the form asks for, on the wall they are taken from. Fitting height runs from the pole to the floor, not from the top of the window. The header adjustment is measured to the pole for eyelet curtains, which sit above it, and to the hook for pleated ones, which hang below the ring — so it can be negative.

Measure from the correct point for your heading. Eyelet and tab-top curtains hang from the pole itself; pencil pleat and pinch pleat hang from the hooks, which sit below the rings.
Measure at both ends and in the middle. Floors and ceilings are rarely level, and you should work to the shortest measurement.
Decide the finish first: 1 to 2 cm clear of the floor for everyday curtains, sill length ending 1 to 2 cm below the sill, or a deliberate puddle of 10 to 20 cm.
Fit the pole or track before measuring. Guessing its height is the other common source of error.

Where to put the pole

The usual guidance is 10 to 15 cm above the window and extending 15 to 20 cm beyond each side. Higher makes the window look taller; wider lets the curtains stack back off the glass so more light comes in. Both matter more than most people expect on a small window.

How this calculator works

A subtraction and an adjustment:

Finished drop = fitting height above floor − floor clearance + header adjustment

The header adjustment allows for the distance between the pole and the top of the fabric. For eyelet curtains the fabric sits above the pole, so the adjustment is positive; for hooks hanging below rings it may be negative.

The result is the finished drop of the made-up curtain, not the fabric length — hems and headings add to that, and a pattern repeat adds more.

Worked example: a pole at 220 cm

Using the default figures — a fitting 220 cm above the floor, 1 cm clearance, no header adjustment:

Finished drop: 220 − 1 = 219 cm

Ready-made curtains come in fixed drops, commonly 137, 183 and 229 cm. A 219 cm requirement falls awkwardly between the last two: 183 cm leaves the curtain 36 cm off the floor, and 229 cm puddles by 10 cm. Either take up the longer pair, lower the pole, or accept a deliberate puddle — which is a decision worth making before ordering rather than after.

Common mistakes

Measuring from the window rather than the pole. The drop starts where the curtain hangs.
Measuring before fitting the pole. Its height is an input, not an assumption.
Measuring at one point only. Work to the shortest of several measurements.
Ignoring the heading type. Eyelet and pencil pleat start from different points.
Forgetting the radiator. Full-length curtains over a radiator send heat straight up behind them.

Frequently asked questions

Should curtains touch the floor?

It depends on the look and the use. A 1 to 2 cm gap keeps them clean and lets them draw easily, which suits everyday rooms. A slight break where the fabric just touches looks more tailored. A deliberate puddle of 10 to 20 cm is a decorative choice for rooms where curtains are rarely drawn. Sill-length is normal above a radiator or a deep sill.

Can I shorten ready-made curtains?

Usually, and it is a straightforward job if the hem is generous — most are. Lined curtains are more work because the lining hem should sit slightly shorter than the face fabric. Hemming tape is a reasonable non-sewing option for a small adjustment. Lengthening is far harder, so if you are between sizes, buy long.

What is the difference between drop and fabric length?

Drop is the finished visible length once made. Fabric length adds the heading allowance at the top and the hem at the bottom — commonly 15 to 25 cm in total, more for a deep double hem — plus an allowance for matching the pattern repeat across panels.

Does the curtain heading affect the drop?

Yes, substantially. Eyelet curtains sit with the fabric top above the pole, so the drop is measured from the pole's top. Pencil pleat and pinch pleat hang from hooks in rings, so the fabric starts several centimetres below the pole. The same pole with different headings needs different drops.

Is what I enter stored?

No. Measurements are processed in your browser and never transmitted or retained.

Related tools

References

GOV.UK — product safety rules, including blind and curtain cord safety for children
Health and Safety Executive — safe use of steps and ladders when fitting poles and tracks

Sources are checked at publication and can change — how I choose and check references.