Leathercraft Guide

On this page you will find some helpful reference information about leather for use by leatherworkers.

Leather Thickness Conversion


Traditionally leather is measured in ‘ounces’, confusingly not a measurement of weight but of thickness. Ounces is really quite a useless measurement as it doesn’t directly relate to any other measurements which you will use however it is still used out of tradition.

In the UK you may find leather for sale by mm or by ounce, in the US it will be predominantly by the ounce (in other countries I’m not sure what you will find). Either way you must know how to interpret both types of measurement.

Leather is almost always sold in a range e.g. ‘8-9oz’ or ‘3.2-3.6mm’, this is because leather varies across a piece and will never be completely exact or consistent enough to simply give it a measurement such as 3.5mm (as you could with steel or wood).

To the left is a table of conversion from ounce to mm, remember that 1oz = 0.4mm so as long as you know your 4 times table you can easily convert this in your head (6x4 = 24, 6oz = 2.4mm and so on).

I have also included fractional inches in the table although you are unlikely to see leather for sale by those, 1 ounce = 1/64inch.

Parts of the Hide

Depending on the animal in question a hide or skin may be sold in whole or in part. Examples of skins which will almost always be sold in whole are all small animals such as snakes, rabbits, stingrays etc. You may also often buy a whole hide for smaller animals such as a kangaroo, or for young animals e.g. calf skins.

For a larger animal (most commonly a full grown cow) the leather can be bought by the hide or by a cut (subsection) of the hide.

Factories making leather goods or large scale producers may buy whole large hides but the home leatherworker often may not as they are big and expensive (see below for sizing guide).

Different manufacturers may refer to the same cut as different things so where possible I have included alternate names. Click on each cut name in the list to show the leather included in the diagram:

Sizes of Cuts

leather hide cut sizes

A whole cowhide may be more than many leather workers need to buy at once or have space to process (the image below shows two sides which when laid out take up my whole lounge floor nearly).

Remember that all the leather you buy also has to be stored somewhere! On the left you can see the sorts of sizes which different cuts of a hide may give you (not to scale).

leather whole cowhide

Of course, no two animals are alike so the yield will vary from animal to animal, these are some averages only for cowhides which will be the most common.

When you buy your leather it may usually be sold by the square foot. This is often referred to as ‘by the foot’ though you are buying by area not length as you would with fabric.

If a company sells by the square foot then your piece will cost the foot price multiplied by the piece size e.g. 14ft2 @ £8/ft2 = £112

Other companies such as Tandy Leather now price by the piece to make things simpler, so you may be able to buy a double shoulder with an average yield of 15ft2 but whether the piece you get is 14ft2 or 16ft2 it will cost exactly the same. Companies selling in this way should err on the side of the customer and in general you should be getting at or above the stated size rather than below.

leather square footage

Remember that the size is not measured by the extremities of the piece, tanneries have machines which can scan a piece of leather and then mark it with an accurate size.

For example a piece may fit roughly into a 2'x6' rectangle but it could be marked as 10.8ft2 (rather than 12ft2) due to irregular edges. When you receive a piece of leather you may be able to see this measurement marked on the flesh side, this is what the shop will refer to when selling you your piece (see image to the right).

Waste and Scrap Leather

With all leather pieces there will be waste, it’s just not possible to use every scrap of leather that you buy. This waste may be:

  1. cutting waste i.e. the pieces between the parts you cut or left over shapes that you can’t use
  2. scrap or unusable leather included in your piece
bridle butts

All cuts of leather will have cutting waste (which can be minimised with careful cutting and planning) however the amount of scrap leather will vary by the cut.

For example a bend/butt is the best part of the hide and doesn’t include any scrap leather such as belly/cheek etc., in other words you should be able to use just about all of the leather which you receive.

Pictured to the left are two bridle butts, as you can see almost the entire piece is usable leather except the very tail section to the top of the image (which was kept really to give the tannery somewhere to hang the pieces as you can see by the holes).

Other cuts such as a shoulder may include some cheek and foreleg parts on the edges which will be stretchy, marked, rough to the flesh side and generally unusable.

Whichever cut you buy you will be paying for the whole thing though, in other words with certain cuts you’re paying for leather which you will never use. However, the better cuts are inherently more expensive so it balances out in the end.

Remember that some scraps can be kept and used for small projects, testing stamps, testing the sharpness of tools, testing dyes etc. but be realistic and bin anything which is unusable.

Vegetable vs Chrome Tanned Leather

Vegetable Tanned Chrome Tanned
time to tan6-12 months1 day
costmore expensive
suitable for
yes (if unfinished)no
sold byhides/cutsusually full hides
  • sheaths
  • holsters
  • belts
  • cases
  • wallets
  • bags
  • etc.
  • shoes
  • upholstery
  • automotive
  • clothing
  • etc.
temperstronger/firmersofter/more supple
usually russet (natural)
plus browns and black
wide variety including
bright colours
requires finishesnaturally good
ageingwill age well
and patina
will usually stay
flat looking
damages metalsgenerally notmay tarnish metals
due to chemical content
smellgenerally a nice
leathery smell
largely odourless
of years ago
in the 1850s

Something which can confuse new leatherworkers is the difference between vegetable and chrome tanned leather. What does it mean, what are they used for and which should you buy? The table to the left highlights some key differences.

I will not go into a detailed description of leather tanning here since it will not be of interest to many people, however vegetable and chrome (or mineral) tanning refers to how a hide is treated beyond a certain point in the process. So most animals after slaughter and skinning will have the hides reduced to rawhide via a series of processes such as hair removal, defleshing and so on. Once the rawhide is made it can be left as rawhide (a stiff leather which is used for things like dog chews but not too often by leatherworkers) or tanned.

During vegetable tanning the leather, over a period of months, is steeped in a solution of barks, plant extracts or similar materials to create beautiful, high quality, nice smelling leather which we often use in leatherwork. The solution will vary from tannery to tannery and will give different properties to the final leathers (colour etc.). This is a lengthy process and as such increases the cost of the leather.

This leather may be further refined (curried) with dyes and finishes to create something like a bridle leather which is ready to use or it may be left as it is and sold as natural tooling leather for the leatherworker to dye and finish as they wish. It may also just be dyed in which case it can still be stamped but will also need finishing.

During chrome tanning the leather is put into large drums with various chemicals (some of them can be quite nasty) and tanned very quickly, often in as little as 1 day. Usually the leather will also be dyed and finished as chrome tanned leather is generally sold as ready to use and requires no further processing by the leatherworker (or factory more commonly).

Which to Use

There is nothing inherently wrong with chrome tanned leather (aside from environmental concerns), indeed almost all leather produced in the world is chrome tanned, but if you are interested in making your own leather goods it’s unlikely you’ll buy much of it unless you’re making clothes.

Veg tanned is more closely associated with leather craft and chrome tanned is more associated with industrial manufacturing. As leatherworkers the properties of traditional veg tanned leather such as the ability to tool it, the high quality, natural markings and so on are what we like.

Of course there are plenty of high quality chrome tanned leathers also which may be used by high end bag makers and the like (companies such as Hermès), it’s just more often associated with mass manufacturing. As you learn more leatherwork you will understand the uses and differences more; when starting out the chances are you’re after veg tan though.

Identifying Chrome Tanned Leather

Sometimes people say they have found or have been given a bit of leather and are unsure of the type. Using the information above including smell, source, colour etc. should help you to identify the type. There are a few other giveaways which will tell you if leather is chrome tanned:

  • a blue/grey coloured band running through the middle of the leather
  • will not accept a stamp when dampened down
  • place a small piece in boiling water - veg tanned leather will shrivel up where as chrome tanned leather will not
  • burn a small piece with a lighter (outside) - veg tanned leather will not catch fire and will create grey or black ash where as chrome tanned leather may burn more easily and create green ash

Thread Sizes

mm Tiger
(Ritza 25)
Fil Au Chinois
Lin Cable
Coats Barbour

This section helps you to compare hand sewing threads, please note that I do not have any information on machine threads as I don’t own one!

Different companies use different measurements to indicate the thickness of their thread. To compare two threads where both are measured in something sensible is easy; we know that 0.5mm thread is a bit lighter than 0.6mm thread and so on.

But what if you want to compare some 18/4 linen thread to some 632 Fil Au Chinois thread … not so easy! To the left I have made a table showing some common sizes and makes of thread to make comparison as easy as possible.

Linen thread sizes are the most confusing of all, they are traditionally measured as gauge/ply e.g. 18/3 means 18 gauge thread with 3 strands twisted together. If you had 18/4 each strand would be the same thickness but there would be 4 strands not 3, so the overall thickness would be greater. When needing a lighter or heavier thread you could increase or decrease both the gauge and ply count so comparing them quickly becomes difficult.

The gauge of linen thread is a measurement of the length that can be spun from a standard unit, so as the gauge increases the size of the thread decreases. In other words a bigger gauge is smaller thread i.e. 20/3 is smaller than 18/3. Most companies producing linen thread do not seem to publish a mm equivalent and sizes seem to vary from company to company so the linen info in the table (except the Lin Cable thread) may not be totally accurate.

Where possible I stick to using Tiger Thread as it is the best thread you can buy in my opinion. I do also use the Fil Au Chinois for some items as it comes in a broader range of colours though it's not as resilient.

Stitch Sizes

spi example items thread size needles
  • watch straps
  • very fine work
0.5-0.6mm john james 004
  • wallets
  • slips
  • small cases
  • notebooks
0.6-0.8mm john james 004
  • knife sheaths
  • holsters
  • large bags
  • pouches
  • guitar straps
0.8-1mm john james 002
5 or less will not look good and
should be avoided
1mm or above  

When hand stitching leather you can choose to shorten or lengthen your stitch to suit the item which you are making. The measurement that we use for this is stitches per inch, often shortened to ‘spi’.

There are two considerations to make here; firstly the size of the stitch should match the item and secondly the size of your thread should match the size of your stitch.

So for example a watch strap might be stitched at 10spi with a 0.5mm thread, a gun holster might be stitched at 6spi with 1mm thread. The strap would look ridiculous done at 6spi with bulky thread and the holster would not be strong enough done at 10spi with the thin thread, hence you can see how these things must be matched appropriately.

Generally speaking the more stitches per inch you have the finer the work is referred to as being. Smaller stitching is a hallmark of higher end items and overly large stitching can tend to make items look a little more amateurish. Above all though the neatness and consistency of the stitch and integrity of the item is of utmost importance.

Having said that there are no hard and fast rules. People often say ‘what should I stitch this project with?’ to which my answer will always be ‘something appropriate’. As long as your spacing and thread size are appropriate then it’s not a problem, there is always some choice and leeway. In the table are some guidelines only as to suggestions for thread and spacing for some common items which you can use as a starting point.

pricking iron and wheel sizes

SPI Seiwa Craft Sha Vergez
Tandy etc.
12No. 12
11No. 11
10No. 10
9No. 9
8No. 8No. 8
7No. 7No. 7
6No. 6No. 6
55mm2.5mmNo. 5No. 5
4No. 4
3No. 3

If you buy an overstitch wheel and wish to to mark your stitches that way it will be sold in spi, i.e. a number 6 will be 6spi.

If you buy a pricking iron, either the marking type or the hammer through type (which some people called a diamond stitching chisel or some such), then it may be sold either in spi or mm.

If it’s sold in mm then the mm measurement may refer to either the distance between the points which equates to the stitch length or the distance in between each prong which is commonly half the stitch length.

All types of pricking irons are also sold with different numbers of teeth/prongs, all you really need is a 2 prong for curves and then a 6-10 prong for doing straight bits (these irons must have the same spi or the stitch will look different in the corners).

To find the spi of an iron which uses mm divide 25.4 (the number of mm in one inch) by the stitch length e.g. a 3mm iron gives ~8.5spi (25.4/3 ~= 8.5).

The table to the left shows you the common sizes of irons and wheels available and how they compare. The image below shows you how different real world stitching looks as the size of the thread and stitch increase.

leather stitching