Fabric Half Drop Pattern Repeat Explained

HALF DROP PATTERN REPEAT FABRIC

By defining a standard pattern repeat and a half drop pattern repeat below it should become obvious what a half drop pattern repeat is and why half drop pattern repeat fabrics require different cutting and fabric calculations.

STANDARD (VERITCAL) PATTERN REPEAT

In our tutorials when cutting patterned fabric we increase the length of fabric we cut to a whole number of pattern repeats and cut at the same point on the pattern so the cut drops are identical and match when joined together . This is called an ADJUSTED CUT DROP. Most fabrics have a standard pattern repeat and join using this method.

In the following example of a STANDARD PATTERN REPEAT you will see the pattern is the same on both sides of the fabric roll, and aligns perfectly when 2 adjusted cut drops (identical panels 3 pattern repeats (PRs) long) are side matched.

HALF DROP PATTERN REPEAT

With a half drop pattern repeat fabric this method doesn't work.

The pattern doesn’t match exactly on each side of the fabric roll and matches half a drop down instead. See in the diagram how the fabric doesn’t match if you again cut 2 identical panels of fabric at the same place on the pattern 4 PRs long and align the cut panels.

The second panel needs to be shifted half a pattern repeat up or down for the identical panels to match.

Quick Video Explaination

HOW CAN I TELL IF MY FABRIC IS A HALF DROP PATTERN REPEAT?

Your fabric supplier should specify if the fabric you are purchasing is a half drop pattern repeat and what the full (whole) vertical pattern repeat is.

In our experience an example of how fabric suppliers would describe a half drop pattern repeat fabric would generally be "Pattern Repeat: 62cm Half Drop".

This usually means the whole pattern repeat is 62cm and the fabric is a half drop pattern (half a pattern repeat would be 31cm). If you have any doubt what the whole pattern repeat on the fabric is, you need to either measure it on the fabric or clarify it with the supplier if you don't have the fabric yet.

CALCULATING FABRIC QUANTITY

A half drop pattern repeat will affect the calculation of the fabric quantity required and the order in which fabric panels are cut and joined to make a curtain or blind. There are 2 methods we use in the workroom to calculate half drop pattern repeats to ensure the minimum wastage of fabric.

The first we call the "ODDS & EVENS- WHOLE PATTERN REPEAT" method. This is used when the adjusted cut drop rounds up nearest to a whole pattern repeat rather than half a pattern repeat (cut drop is more than half a PR into the next pattern repeat). It is the simplest method and works in all cases.

For example if the fabric cut drop was 210cm and the fabric pattern repeat 55cm half drop. Then number of pattern repeats the fabric cut drop would cover would be 210/55 = 3.82 pattern repeats (PR). In this case we would use the ODDEVEN method as it is more than 0.5 into the last PR (it is 0.82).

The second method we call the "A & B - HALF PATTERN REPEAT" method and is used if the cut drop is less than half a pattern repeat into the next pattern repeat. This method has a couple of situations where you will need an extra half a pattern repeat to get your panels to join correctly, but can save significant amounts of fabric compared to the "ODDS & EVENS" method if your fabric cut drop has just gone into the next pattern repeat.

For example if the fabric cut drop was 210cm and the fabric pattern repeat 50cm half drop. Then number of pattern repeats the fabric cut drop would cover would be 210/50 = 4.2 pattern repeats (PR). In this case we would use the AB method as it is less than 0.5 into the last PR (it is 0.2).

This method rounds the fabric cut drop up to a whole number of pattern repeats so is the best method when the cut drop is more than half way into the last pattern repeat.

FABRIC QUANTITY CALCULATION

The fabric quantity calculation is essentially the same as with a standard pattern repeat fabric. The fabric cut drop up is rounded up to the next whole pattern repeat to calculate the ADJUSTED CUT DROP.

Calculate the ADJUSTED CUT DROP (ACD) in whole pattern repeats
Mutliply ACD by number of widths (drops)
Add one whole pattern repeat to total

EXAMPLE CALCULATION 1

Pair of curtains, 5 widths, fabric cut drop 189cm, PR 73cm half drop
189cm/73cm = 2.59 therefore ACD = 3PR
ACD = 3 x 73cm = 219cm
Fabric QTY = (219cm x 5) + 73cm (1PR) = 11.68m

It is crucial you add the one whole pattern repeat to the total. You will be using half of this whole pattern repeat to position* the pattern and the other half to compensate for the half drop pattern repeat when cutting the fabric drops.

*We recommend using only half a pattern repeat for positioning to save fabric costs. Half drop pattern repeats are generally large and the have a staggered repeat half way down the pattern repeat already, so half a repeat usually works fine for positioning the pattern. In some cases you may want to add another half PR to the total fabric qty to give you a whole PR to position the pattern.

MEASURING AND CUTTING FABRIC

We number the drops, eg if there are 5 drops they are numbered 1,2,3,4,5.

Each drop will be cut to the length of the ACD except for the LAST ODD DROP (in this case drop 5) which will be half a pattern repeat longer. The order you cut the drops and how you cut them is important to compensate for the half drop pattern repeat.

METHOD

Calculate the ADJUSTED CUT DROP (ACD) in whole pattern repeats (rounding fabric cut drop up to next whole pattern repeat)
Number each drop that will be required eg: drop1, drop2, drop3 etc
Find the position on the roll to start measuring your drop from so the pattern falls on the blind or curtain where you want it. (only use up to half a whole pattern repeat for this).
Measure and cut all your odd numbered drops and label them. (1,3,5 etc) first. Each odd drop will be the length of the ACD except the LAST ODD drop which you cut HALF a whole pattern repeat longer. This will put you at the correct position on the fabric to start measuring and cutting the even numbered drops.
Next measure and cut all your even numbered drops the length of the ACD and label them.(2,4 etc).
See the diagrams below for how to join the drops.

Example cutting 5 drops (ACD 3 Pattern Repeats).

You have basically cut half the drops first (odds) then shifted along the fabric an extra "half a whole pattern repeat” before then measuring and cutting the remaining drops (evens).

JOINING THE DROPS

After cutting your required number of drops using the principle above you will have 3 types of cut length of fabric, ODDs, EVENS and LAST ODD. You should find when you come to join your numbered drops, odd and even drops align. After joining the drops trim the extra half pattern repeat off the end of the last odd drop.

JOINING COMBINATIONS

The following diagrams show the joining combinations of the panels using the ODD EVEN method when you have from 2 to 8 drops.

This method rounds the fabric cut drop up to the nearest half pattern repeat so is the best method when the cut drop is up to half way into the last pattern repeat.

FABRIC QUANTITY CALCULATION

Calculate the Adjusted Cut Drop (ACD) by rounding the cut drop up to the next HALF Pattern Repeat (PR) not whole PR.
Multiply the ACD by the number of drops and add half a PR* to position the pattern to calculate the total fabric required. *NOTE if you are making a pair of curtains with an odd number of drops add a whole PR instead of half a PR as you will need an extra 1/2 PR to align the split width on the curtains.

EXAMPLE CALCULATION 1

Pair of curtains, 4 widths, fabric cut drop 189cm, PR 90cm
189cm/90cm = 2.1 therefore ACD = 2.5PR
ACD = 2.5 x 90cm = 225cm
Fabric QTY = (225cm x 4) + 45cm (half PR) = 9.45m

EXAMPLE CALCULATION 2

Pair of curtains, 5 widths, fabric cut drop 189cm, PR 90cm half drop
189cm/90cm = 2.1 therefore ACD = 2.5PR
ACD = 2.5 x 90cm = 225cm
Fabric QTY = (225cm x 5) + 90cm (whole PR) = 12.15m

Note the difference in example 1 with 4 widths (drops) 1/2 a PR is added. But 1 PR is added in example 2 because it is a pair of curtains with an odd number of widths (drops)

MEASURING AND CUTTING FABRIC

Use up to 1/2 PR* to position the top of the first drop.
Cut the Adjusted Cut Drops (ACDs) marking them alternately A then B. If you are making a pair of curtains with an odd number of drops, cut the last drop (which will be an "A" half a PR longer. You will have included an extra half PR in your fabric qty calculation for this purpose.
Use the diagram below to join the drops.

Example cutting 5 drops (ACD 2.5 Pattern Repeats).

The above example demostrates you have to add an extra half pattern repeat to the last "A" when making a pair of curtains with an odd number(5) of drops. See in the diagrams below how the drops from these examples are joined to form the 5 width single curtain and the pair 2.5 widths each.

JOINING COMBINATIONS

The following diagrams show the joining combinations of the panels using the A B method when you have from 2 to 8 drops.

Check your calculations on our Half Drop Pattern Repeat Calculator

The calculator will determine which method saves the most fabric, calculate your cut drops, total fabric quantity, create a cutting diagram and panel joining diagram