Convert yd to cm

A yard is three feet, and outside American football and fabric shops it is a unit most people rarely meet. It is defined as exactly 0.9144 metres.

Centimetres are the everyday metric length — body measurements, paper, furniture — and they are the one metric unit that has no direct customary counterpart, which is why so much converting happens through them.

The factor is 91.44, and almost nobody carries that around. Rounded to 91 it is off by 0.48 % — which stays invisible on small numbers and turns into a whole unit somewhere around 1,000 yd.

That is the number worth knowing before you round: not the error itself, but where it stops being ignorable. Below that point the shorter factor is the sensible one; above it, use the field above, which never rounds until it prints.

The yard has been defined in metric terms since the international yard and pound agreement of 1959, and in this page's units that comes out at 91.44 cm to one. The definition is exact by stipulation — it was not measured, and it cannot be refined by measuring it better. The decimal above is the whole of it, with nothing rounded away at the end.

Before that agreement the US and the British versions differed slightly, and old survey figures still carry the older definition. For anything outside land surveying the difference is far below the precision anybody is working to.

The whole difficulty of this conversion is that the two units are close enough to be swapped without anybody noticing at the counter. A yard is 91.44 cm; a metre is 100. The gap is 8.56 cm per unit, which on a three-yard requirement is nearly 26 centimetres — the difference between having enough cloth for a facing and not having it.

The direction of the substitution decides whether it is harmless. Buying metres where yards were asked for always gives you more than you needed, so it fails safely and costs a little money. Buying yards where a metric requirement was written always gives you less, and it fails at the point where the last pattern piece will not fit on what remains. If in doubt about which system the requirement came from, buy in metres.

Fabric is sold as a length off a roll of fixed width, so a requirement of two and a half yards is meaningless until you know how wide the bolt was. American quilting cotton is 44 or 45 inches, which is 111.8 or 114.3 cm; dress and furnishing fabric is frequently 60 inches, or 152.4 cm. European bolts are commonly 140 or 150 cm. The width is printed in the pattern’s requirements, usually in a line most people read past.

A wider bolt does not save length in proportion to its width, because pattern pieces are rigid rectangles laid on a grid rather than area to be poured. Going from 114 cm to 152 cm often saves a third of the length on a garment with small pieces and saves nothing at all on one with a full-width skirt panel. The only reliable way to recalculate is to lay the pieces out on the new width, on paper or on screen, and measure what they reach.

When the width changes, start from the widest piece rather than from the total. If the longest pattern piece is 60 cm wide, two of them fit side by side across a 114 cm bolt with 6 cm to spare and three fit across a 152 cm one only if the piece is under 50. That first check decides how many rows the layout needs, and the number of rows, not the area, sets the length.

Then add for the things a yardage figure quietly includes: matching a repeat, cutting with the nap running one way on velvet or corduroy, and cutting on the bias. A one-way layout can add a fifth to the length, and a large print repeat can add the length of the repeat itself. Convert last, after the layout is settled, so that the centimetre figure you take to the shop is the one you actually need rather than a converted guess.

Quilting is built entirely on the quarter-inch seam allowance, and a quarter of an inch is 6.35 mm. Metric rotary rulers are marked in millimetres and half centimetres, so the natural substitution is 6 mm or 0.5 cm, and both are wrong in the same direction. Six millimetres takes 0.35 mm too little cloth on each side of every seam, which leaves 0.7 mm in the work per join.

Over a block that is nothing and over a quilt it is everything. Twelve seams across a row add about 8 mm, so a block that should finish at 12 inches finishes nearer 12 3/8 and will not meet its neighbours. The fix is not to convert more carefully but to work in one system throughout: either cut and sew in inches with an inch ruler and a quarter-inch foot, or use a pattern drafted in centimetres with a 7 mm allowance designed for it. Mixing the two is where the drift comes from.

The same fixed-width problem turns up at a far larger scale in flooring. American broadloom carpet and sheet vinyl come off a roll twelve feet wide — 3.658 m — and are sold by the linear yard, so a price per yard is a price for 91.44 cm of a 3.658 m strip. A European room specified in metres has to be laid out against that width before any length can be ordered.

The seam position is what the conversion is really for. A room 4.2 m wide cannot be covered by one 3.658 m width, so it needs a second piece and a seam, and where that seam falls decides how much extra length is needed to match a pattern across it. Converting the room to yards first and the roll to yards second, then doing the layout in one unit, avoids the common error of comparing a metric room dimension against an imperial roll width by eye.

Patterns quote fabric requirements in eighths of a yard, because that is the smallest amount a shop will cut. An eighth of a yard is 11.43 cm, so any requirement has already been rounded up by as much as that before it reached you. Converting 2 3/8 yards into 217.17 cm and asking for it to the millimetre asserts a precision that never existed in the original figure.

Round the converted number up to a sensible cutting quantity instead — the next 10 cm is the usual convention in a metric shop, and many will not cut less than 25 or 50. Keeping a little more than the arithmetic demands is also the only insurance against the two things this conversion cannot predict: a bolt cut slightly off square, and shrinkage on the first wash, which on cotton can take two or three per cent of the length before you have cut anything.

Working in the other direction, ask for the imperial quantity that covers your metric one rather than converting at the counter. Two metres is 2.19 yards, so ask for two and a quarter — 205.74 cm — and you have 5.7 cm of margin. Three metres is 3.28 yards, so ask for three and three eighths. Doing the rounding yourself, in advance, is what stops a cut being made to the nearest quarter-yard below what you needed.

Precut quantities carry their own names and their own conversions. A fat quarter is 18 by 22 inches, or about 45.7 by 55.9 cm, and a fat eighth is half of that; both come from a 44-inch bolt and neither is a strip. A metric shop selling something called a fat quarter is usually cutting 50 by 55 cm from a 110 cm bolt, which is a slightly different piece with the same label — worth checking when a pattern specifies a count of them rather than a length.