How To Size Up A Sewing Pattern: A Simple Guide To Grading

It is the question we are asked more than any other, on almost every pattern we publish. The pattern runs to a size 18 and you need a 22. Or it starts at a size 8 and you are a 4. Somebody always asks, and the honest answer has always been a slightly apologetic “you can grade it up yourself”, which is not much help if nobody has ever shown you how.

So here is the showing. Grading a pattern is not difficult and it does not need any special equipment. What it does need is a little care in the right places, because there are two or three points where it quietly goes wrong and you do not find out until the garment is cut.

First, Make Sure You Actually Need To

A surprising number of people grade a pattern they did not need to touch, because they compared their body measurements against the wrong numbers.

Most of our patterns list finished garment measurements, which is how big the finished thing is, not how big you are. The difference between the two is called ease, and it is deliberate. A fitted dress might have two inches of ease at the bust so you can move and breathe. A loose cardigan might have eight or ten inches, because it is meant to hang open and drape.

So before you cut anything, do this:

1. Find the finished garment measurement for the largest size in the pattern.
2. Measure your own body at the same point.
3. Subtract. That difference is the ease you would get.
4. Compare it to a garment you already own and like the fit of.

If the largest size gives you three inches of ease at the bust and the top you wear every week has two, you do not need to grade at all. Cut the largest size and enjoy your afternoon.

And if it is only your bust that does not fit

This is worth separating out, because it catches a lot of people. If your shoulders, back and hips sit comfortably in the size but the bust is tight, sizing up the whole pattern is the wrong fix. You will end up with a garment that gapes at the neck and hangs off your shoulders in order to fit one part of you.

What you want instead is a full bust adjustment, which adds room exactly where it is needed and leaves everything else alone. We have a complete walkthrough of it, and it is the more useful skill of the two.

Measure Yourself Properly First

Nearly every grading problem starts with a bad measurement. It is worth five minutes to get these right, and it is much easier with somebody helping you.

Tool Tips: Budget Or Quality? Tape Measures

• Bust: around the fullest part, with the tape level all the way round, including across your back. This is the one people most often get wrong by letting the tape drop at the back.
• Waist: the narrowest part of your torso, which is usually higher than where you wear your trousers. Bend sideways and the crease that forms is your waist.
• Hips: around the fullest part, usually seven to nine inches below the waist. Include your seat, not just your hip bones.
• Back length: from the bone at the base of your neck down to your waist. This one decides whether a bodice sits where it should.

Wear the undergarments you intend to wear with the finished garment, keep the tape snug but not pulled tight, stand normally, and do not hold your breath. Write the numbers down. Measure again in six months, because bodies change and a chart you wrote in 2019 is not you.

Work Out How Much To Add

Look at the pattern’s own size chart and work out how much it grows between one size and the next. On most of our patterns the bust grows by roughly one and a half to two inches per size, so going up one size means adding about two inches to the total bust measurement.

Here is the part that trips everybody up, so read it twice.

The amount you add to a pattern piece is not the amount you want to gain. A pattern piece is usually half the garment, and often you cut two of them. So if you want two inches more around your bust, and the garment has a front and a back, you are adding two inches spread across four vertical edges. That is half an inch at each edge.

The arithmetic is always the same:

• Decide how many inches you want to gain in total, all the way around.
• Count the vertical seam edges the garment has at that level. A simple top with a front and a back has four, two at each side seam.
• Divide the first number by the second.
• That is what you add at each edge.

Two inches gained, four edges, half an inch each. Four inches gained, four edges, one inch each. If your garment has a centre back seam as well, that is six edges, not four.

Method One: The Seam Edge Method

This is the quick way, and for a lot of what we publish it is perfectly good.

Use it when: the garment is loose or unfitted, has no closure and no waist seam, and you are going up one or two sizes. Cardigans, boxy tops, elastic waist skirts, simple shift dresses and most childrenswear all qualify.

How to do it: tape a strip of paper along the side seam edge of the pattern piece. Mark your added amount out from the existing cutting line at the bust, at the waist and at the hip. Join those marks with a smooth line that follows the shape of the original edge rather than cutting straight across it. Do the same on the front and the back, and add the same amount to the underarm seam of the sleeve so the sleeve still fits the armhole.

Blend the new line back into the original at the armhole, and do not change the armhole curve itself. That is the whole method.

Where it falls down: everything grows at the side seams and nothing grows anywhere else. Your shoulders, neckline and armhole depth stay exactly as they were. Go up more than about two sizes this way and the garment starts to look wrong: wide through the body, but with a neckline and shoulders that belong to a smaller person.

Method Two: Slash And Spread

This is the proper way, and it is what pattern companies do. It grows the piece in both directions at once, so the proportions hold.

Use it when: the garment is fitted, has a waist seam, buttons or a zip, set in sleeves that matter, or when you are going up more than two sizes.

1. Trace the pattern piece onto fresh paper, because you are about to cut it up and you will want the original.
2. Draw one vertical line from the shoulder down to the hem, roughly through the middle of the piece, and one horizontal line across it at about the level of the armhole notch.
3. Cut along both lines. You now have four sections.
4. Slide the sections apart on a fresh sheet. Spread the vertical gap by the amount you calculated for that edge. Spread the horizontal gap by a smaller amount, usually a quarter to a half inch per size, to add length through the body.
5. Keep everything square. The pieces must stay parallel, so use the grainline as your reference and check it with a ruler.
6. Tape it all down and redraw the outline as one smooth continuous line, easing over the little steps where the sections meet.

The redrawing at the end is the part that matters. A graded pattern that still has visible steps in the cutting line will produce a garment with visible steps in the seam.

How Far Can You Push It

Two sizes is the honest limit for home grading, and that is roughly three to four inches on the bust.

Beyond that, the proportions stop being a matter of adding width. Real commercial grading changes armhole depth, shoulder slope, neckline width, dart size and sleeve cap height, all by different amounts, and it does so differently at the larger end of the range than the smaller. If you need four sizes, you will usually get a better garment by starting from a pattern that is drafted for your size, or by making a sloper from your own measurements. Our post on making a pencil skirt sloper shows the principle on a simple garment.

The looser the garment, the further you can push this. An unfitted cardigan will tolerate a lot. A tailored jacket will not tolerate much at all.

The Bits People Forget

Four things get missed almost every time, and each one turns a good grade into a wasted afternoon.

Altering sleeves and truing the pattern – Sew the Perfect Fit

• The sleeve. If you widened the bodice at the underarm, the armhole got bigger, so the sleeve has to grow to match. Add the same amount to the sleeve underarm seam. Then walk the seams: measure the armhole edge and the sleeve head with your tape on its edge and check they still match, allowing for whatever ease the sleeve had originally.
• Facings, bindings and waistbands. These are cut to fit an edge that has just changed length. Re-measure the edge on your new pattern and cut them to the new length. This is the single most common reason a graded garment will not go together at the last step.
• Seam allowances. If you added to the cutting line, the seam allowance came with it and everything is fine. If you added to the stitching line, you now need to add the allowance back. Know which line you are working from before you start.
• The hem sweep. Widening at the side seams on an A line shape adds far more at the hem than at the bust. Check the finished hem width is still something you want to wear rather than something you trip over.

Make A Toile. Really.

Nobody wants to hear this and everybody who skips it regrets it eventually.

Making a muslin, bodice pattern adjustment – Sew the Perfect Fit

You do not need to make the whole thing. Cut the bodice only, or the top half of the garment, from an old sheet or the cheapest cotton in the shop. Baste the seams with a long stitch. Put it on. You will learn in about ninety seconds whether the armhole binds, whether the shoulders sit right and whether the waist lands where your waist actually is.

Mark any changes on the toile with a pen, unpick it, and lay the pieces back on your pattern to transfer the corrections. Half an hour on an old sheet against three metres of fabric you loved is not a difficult trade.

Five Mistakes To Avoid

• Adding the full amount at each edge. Wanting two inches and adding two inches at all four side edges gives you eight inches. Do the division.
• Grading from body measurements instead of finished measurements. You will add ease on top of ease and end up in a tent.
• Letting the grainline drift. When you slash and spread, if the sections rotate even slightly the garment will twist on the body and you will never work out why.
• Forgetting the pattern is half the garment. A piece cut on the fold is half. Two pieces cut from one pattern is still only half of what goes around you.
• Grading a pattern that was scaled wrong when printed. Always check the test square first. If it is not a true two inches, nothing downstream will be right. Our guides on printing and assembling a PDF pattern and printing a layered PDF cover this.

The Tools That Make This Easier

You can grade a pattern with baking parchment, a school ruler and a pencil. Plenty of people do, and it works. But a handful of inexpensive things make the job faster and a good deal more accurate, and every one of them earns its keep on each pattern you touch afterwards.

• Swedish tracing paper. The most useful thing on this list. It is see through, so you can lay it over the original and copy the lines exactly, and it is strong enough to sew, so you can stitch your traced pieces together and try the toile on before you cut into fabric. Ordinary tracing paper tears at the fold. This does not.
• A pattern grading ruler. A clear ruler two inches wide and eighteen inches long, marked with a grid. The grid is the whole point: you line it up with the original cutting line and mark a new line a consistent distance away, which is exactly what the seam edge method asks for. Doing this with a school ruler is where wobbly side seams come from.
• A set of french curves. For redrawing the armhole and neckline smoothly once you have spread the pieces apart. A straight ruler cannot draw a curve, and a freehand curve looks freehand. After the tracing paper, this is the one that changes your results most.
• A serrated tracing wheel. Run it along the original cutting line with paper underneath and it perforates a copy of that line, no seeing through required. Useful on heavier pattern card where tracing paper will not sit flat.
• Tailors chalk. For getting your new cutting line onto the fabric. Chalk brushes off and pen does not, which matters on a garment you are still slightly unsure about.
• Pattern weights. Pinning through paper distorts it, and pinning through your traced copy distorts that too. Weights hold everything flat while you draw, and they are much quicker than pinning.

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A Good One To Practise On

If you want to try this on something forgiving, the easy long cardigan is close to ideal. It has no closure, no waist seam and no fitted bust, so the seam edge method works well on it and small errors simply disappear into the drape. It is also free, so a mistake costs you nothing but an evening.

Altering the Easy Pleated Skirt pattern. How to increase or decrease the waistline: Part 4

Grade it up one size, make it in something cheap, and you will have the whole method in your hands. After that, nothing in the pattern library is really closed to you.

If you have a pattern you have been wanting to make in a size we do not offer, tell us in the comments which one. It genuinely helps us decide what to grade properly and re release.

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