Traditional units of measurement are quite versatile.

Throughout history, traditional units (imperial, US customary etc) have been chopped and changed at various times for various reasons. Further to that, there was a time when every country, and even regions within a country, had their own version of what each unit was defined as.

For example, the original Roman mile was defined as 1000 paces (the distance your left foot has travelled in a two step march). It was later decided that a pace was exactly 5 feet, making the mile 5000 feet. Over time, lots of other definitions of a mile came into use across the world. You can’t blame them, there were no iPhones back then. They didn’t even have the Internet, so communication between countries was limited. There was the English mile of 8 furlongs, the Scots had a slightly longer mile, there was an Irish mile that was 27% bigger, the Germans had a mile that was over 212 times bigger than today’s mile, and sea navigators have their own nautical mile.

My point is these units have always adapted to particular needs at certain points in time. They’ve had quite a ‘fluid’ definition. This was fine for the people using those units in that particular place and time, but not so good when it came to international trade, where every country used similar but different definitions of each unit. This is part of the reason for their demise in most countries, as the metric system offered a standard internationally accepted definition for the various measures.

The metric system is now used to measure most things in trade, manufacturing, medicine, science etc; even in the ‘non-metric’ USA. And that makes sense, but as mentioned in my Fancy a Pint? post, some of the traditional units have stuck around. There are some reasons for retaining traditional units as discussed in my Hang on to your Stones post and there are some reasons why the metic system is not perfect for everyday use as I looked at in the Pros and Cons of the Metric System post. If you haven’t read those posts yet, or need reminding, the following are the main weaknesses of the metric system in everyday use;

  • Because of small unit sizes, you often end up with quite large numbers, for example 400g instead of 14oz or 750ml instead of 26 fl oz.
  • The words sound pretty rubbish. Kilogram and kilometre do not sound nearly as good as pound or mile.
  • The prefixes can be cumbersome and unnecessary in everyday use. For example if measuring a plank of wood we would use centimetres or millimetres if using metric. We don’t need the prefixes to tell us the relationship between just two units.

And the following are some of the reasons for ‘Hanging on to your Stones‘  (and other units!)

  • They sound better. Words like pint, gallon, mile and yard sound much better than millilitre, litre, kilometre and metre.
  • (typically) smaller numbers. Using traditional units, you might have 8 oz of something in a recipe instead of 250g.
  • More rational measurements in some cases. For example, using a cup or tablespoon as a unit for portion sizes on a food product would be more easy to visualise than the grams in a portion.
  • They’re part of our history and culture.

With that being said, if we want to retain pounds, stones, pints and miles – how can we do it? What shape does it take? Can it be done alongside the metic system in a non-confusing way? Well, the answers to those questions are not going to appear out of thin air so I guess I’ll make an attempt at answering them.

As I alluded to earlier, units like gallons and pounds have ‘adapted’ throughout history to different ideas of what they should be. I think what should have happened before we went metric (and perhaps still could happen) would have been to re-define these units using the metric system. The following is one example of how this could work.

The tables below show units of weight, volume, length and area redefined based on metric values. For example, a pound is 500g and an ounce is 25g, which means there would be 20 ounces in a pound instead of 16. Not as nice a number I’ll admit, but not unfamiliar — there are currently 20 fl oz in an imperial pint. In each unit, I have attempted to re-align it to a value that is close to their current size so it stays similar to how we currently understand them.

Take a look at the tables below that detail these changes, but don’t stop scrolling — I waffle on for a bit longer towards the end.


The following are for general use.

Fluid ounce (fl oz)

Value Metric
Diff to Imperial (approx) Diff to US (approx)
13.6% smaller (-3ml) 18.3% smaller (-5ml)
For example a 12 fl oz coffee would be 300ml or a bottle of beer could be 12 or 14 fl oz (300-350ml).

Pint (pt)

Value Metric
20 fl oz 500ml
Diff to Imperial (approx) Diff to US (approx)
13.6% smaller (-68ml) 5.7% bigger (+27ml). Previously 16 US fl oz
Cartons of milk, bottles of water etc could move from 500ml to 1 pint, 1 litre to 2 pints etc. To make things easier, pubs could continue to use imperial pints. As long as it’s pretty strict about imperial pints only being used in pubs, I don’t think it would cause confusion.

Gallon (gal)

Value Metric
10 pt 5L
Diff to Imperial (approx) Diff to US (approx)
10% bigger (+454ml). Previously 8 pints. 32.1% bigger (+1215ml). Previously 8 US pints.
For example, large pots of paint, large bottles of oil, cleaners etc. This is the one unit that would be significantly bigger for the USA. It’s not that bigger than the imperial gallon, but the Americans may find it difficult at first! The disadvantage here is that, given the gallon would be 10 pints, the quart would be 212 pints, which isn’t a nice round number. As such it may not be a good idea to use the quart here.

The following are only for use in recipes and portion sizes on foods. For example, rather than using grams for portion sizes on packets of rice, porridge, pasta etc you could use cup measures, which is easier to visualise than if measured by weight.

Teaspoon (tsp)

Value Metric
15 fl oz 5ml
Diff to Imperial (approx) Diff to US (approx)
18.4% smaller (-0.9ml) 1.5% bigger (+0.07ml)
The ‘metric’ teaspoon is already in common use, even in the US (but not always).

Tablespoon (Tbsp)

Value Metric
3 tsp 15ml
Diff to Imperial (approx) Diff to US (approx)
18.4% smaller (-7.7ml) 1.5% bigger (+0.2ml)
The ‘metric’ tablespoon is already in common use, even in the US (but not always).


Value Metric
16 Tbsp 240ml
Diff to Imperial (approx) Diff to US (approx)
13.6% smaller (-34ml) 5.7% bigger (+13ml). Previously 8 US fl oz.
Cups are commonly subdivided into 14, 13, 12, 23 and 34 sizes. ‘Metric’ cups are already in common use in Australia, New Zealand and other countries. You can currently find ‘metric’ cup measures quite easily in shops and online. The value I have given here makes sense because they can be subdivided easily, while keeping rounded metric values. Most current cup measures currently seem to be 250ml, although 240ml is common too. I think either is acceptable, but 240ml (16 Tbsp) makes more sense as it’s closer to the US cup and can be subdivided easier.

The following are for supplementary use, only in specific scenarios. They are of course not really necessary, but are included as supplementary measures because of common usage. A unit from the first table above should appear alongside one of these units, if used.


Value Metric
8 fl oz 200ml
This would only be used optionally in Ireland for bottles of spirits, e.g. 8 fl oz (Naggin).


Value Metric
14 fl oz 350ml
This would only be used optionally in Ireland for bottles of spirits, e.g. 14 fl oz (Shoulder).


Ounce (oz)

Value Metric
Diff to Imperial/US (approx)
11.8% smaller (-3g)
Used in weights for small items. For example, a pot of yoghurt might be 5 oz (currently 125g) or a tin of tomatoes might be 16 oz (currently 400g).

Pound (lb)

Value Metric
20 oz 500g
Diff to Imperial/US (approx)
10.2% bigger (+46g). Previously 16 oz
The smaller ounce and bigger pound mean that we end up with 20 oz in a pound, rather than 16. 20 is not quite as nice a number to work with as 16, but it brings it in line with the pint and I believe it’s worth the sacrifice. It also brings it in line with the 12-inch foot, so if you are quoting your height and weight; both units are subdivided by twelves.

Stone (st)

Value Metric
12 lb 6kg
Diff to Imperial/US (approx)
5.5% smaller (-0.35kg). Previously 14 lb.
Bringing the stone down to 12 lbs makes it closer to the imperial stone (6.35kg) and is also a nicer number (can be halved and quartered into whole numbers, which you can’t with 14).

Ton (t)

Value Metric
2000 lb 1 tonne
Diff to Imperial/US (approx)
1.57% smaller (-16kg). Previously 2240 lb (long ton).
The metric tonne is already in existance and commonly used, so the affect of this would be to simply make the spelling ‘ton’ interchangeable to the ‘tonne’ spelling.


Inch ( ” )

Value Metric
Diff to Imperial/US (approx)
1.6% smaller (-0.4mm)
Used in conjunction with the foot for a person’s height and in dimensions of smaller products. Can be used also in volume and pressure (cu in, pounds per sq in etc).

Foot ( ‘ )

Value Metric
12″ 300mm
Diff to Imperial/US (approx)
1.6% smaller (-4.8mm)
Used for various short distances like a person’s height, road signs or room dimentions etc. Can be used also in volume (cu ft).

Yard (yd)

Value Metric
3′ 0.9m
Diff to Imperial/US (approx)
1.6% smaller (-14.4mm)
Used primarily on roads and walkways for short distances.

Furlong (fur)

Value Metric
225 yds 202.5m
Diff to Imperial/US (approx)
0.66% bigger (+1.3m). Previously 220 yards.
I’m not sure if this would really be used outside of horse racing, but I have included it anyway and rounded up to 225 yds to keep it at 18th of a mile.

Mile (mi)

Value Metric
8 fur (1800 yds) 1.62km
Diff to Imperial/US (approx)
0.66% bigger (+10.6m). Previously 1760 yards.
Pretty much the same as the existing mile. For example, 150 imperial miles would be 151 ‘customary’ miles. As such, existing road signs wouldn’t need to be changed. Miles can be subdivided using furlongs, but it’s more realistic to use fractions such as 14 (450 yds), 13 (600 yds), 12 (900 yds), 23 (1200 yds) and 34 (1350 yds).


Square inch (sq in)

Value Metric
1″ x 1″ 625mm2
Diff to Imperial/US (approx)
3.1% smaller (-20.16mm2)
Not sure where this is used today except for in conversation, but am including it for reference anyway.

Square foot (sq ft)

Value Metric
1′ x 1′ (144 sq in) 90,000mm2
Diff to Imperial/US (approx)
3.2% smaller (-2903.04mm2)
Used commonly by auctioneers or estate agents in quoting room/building sizes. This version would make it easier to convert from m2 (which a builder might give you) to sq ft.

Square yard (sq yd)

Value Metric
1 yd x 1 yd (9 sq ft) 0.81m2
Diff to Imperial/US (approx)
3.2% smaller (-0.026m2)
Used in measuring out rooms etc for flooring. I’m not sure if this is necessary, it may be better to ditch this for sq ft. You could for example have prices for carpet etc marked with prices in both square yards (or feet) and m2

Acre (ac)

Value Metric
5000 sq yd 0.405ha
Diff to Imperial/US (approx)
0.08% bigger (+3.14m2 or +34.9 ‘new’ sq ft). Previously 4840 sq yd.
Rounding the acre up to 5000 sq yd makes it an easier, rounder number to work with, while keeping it pretty much the same as it currently is. Also the conversion to hectares is much easier. Because acres are usually quoted as approximate, this wouldn’t have any real impact.


In addition to the advantages outlined above and in previous posts, the following are some of the advantages of doing this over using the current imperial units;

Less packaging changes

Very few of the packaging sizes would need to change. Most products you buy in the supermarket have been rounded up or down to round numbers in metric units. This would mean if we used these new units, in most cases they would remain as rounded numbers. For example;

  • a 500g bag of sugar would become exactly 1 lb
  • a 200g block of cheese would become an 8 oz block of cheese
  • a 500ml bottle of beer would be 1 pint
  • a 1 litre carton of milk would be 2 pints

There are some cases where some rounding would be needed, like in 454g (1 imperial lb) blocks of butter or 568ml blocks of ice cream.

No changes to exports/imports

An issue we would have if we used imperial units, and an existing issue with US customary units, is that if you want to sell a product in another country that uses only the metric system, they may not be happy with a product that’s say 568ml when all other competitors are at 500ml. This may make your product more expensive and not directly comparable. In that case you may need to create another version of the product specifically for export, which is a rounded metric value. This could add to the cost of production and make the product less competitive. On the other hand, if we used these redefined units that wouldn’t be a problem as they would be the same size anyway, the labels would just need to display a different unit.

Retaining traditional units without being non-metric

I believe this is a way we can retain our traditional units while still being respectful to the fact that we use the metric system. Further to that, the USA has at various times been under pressure to adopt the metric system (which I believe it already has, just not in everyday use) so this could be a way for the US to embrace the metric system further while keeping the units they currently use in everyday life. There are some units omitted here that Americans would use day-to-day like the quart, but of course there’s no reason why they couldn’t be included. I’ll look at the possibility of the USA using this system in more detail in a future post.


As with everything, there are some disadvantages I will now look at.

Requires change

If we implement this, we are changing our understanding of these units. In most cases it doesn’t make much of a difference, especially with the mile, acre, inch etc, but it is a change. Here are some of the most notable changes:

  • The pound is over 10% bigger.
  • There are 20 oz in a pound, instead of 16.
  • There are 12 lbs in a stone, instead of 14 (works out about 5% smaller).
  • The pint is over 10% smaller.
  • There are 1800 yards in a mile instead of 1760.

This may not be a big thing as I would say a lot of people today have a pretty ‘hazy’ understanding of imperial units, considering we haven’t learned them in school for a long time.

Because it’s a different system of measurement, it would require a change to the education system (tetching these units as supplementary to metric) and there would have to be some kind of public education for those of us that are no longer in school. That would of course cost money. As would changing road signs (in the Republic, the UK would not need to change), but there are probably economic ways of doing that by modifying existing signage.

As with any change, there is a risk of confusion. I do believe this can be done in a non-confusing way as long as we define exactly how it should and shouldn’t be used. I will write about how this can be implemented in various areas in future posts.

EU compliance

In order to implement this, we would probably need to ask for permission from the European Union. We converted to the metric system as part of us joining the EU, and the EU have insisted on us completing our metrication over the years, but have softened their view on the topic. In 2007, the EU announced it had put an end to the deadlines for metrication and allowed the continued use of the pint and miles, and other units for supplementary use (see an article on this here). This of course does not mean that we can use imperial as a primary unit but it does mean the EU might allow for this if we ask nicely! Also, the re-alignment to exact metric units and a reassurance it wouldn’t affect any trade, projects, official documentation with the EU would also help.

Where this has been done before

There are instances where this kind of thing is done currently, and has been done in the past.

The Chinese system

The Chinese (a metric country) have units in their measurement system that relate to their traditional system of measures, but have been redefined in exact metric values. For example the tael (or liǎng) is the Chinese equivalent of an ounce, and is exactly 50g. There are 10 tael (500g) in the catty (or jīn), the Chinese equivalent of the pound; and there are 100 catty in a picul (or dàn), the Chinese equivalent of the hundredweight. The engineering world also use metricated traditional units such as the fēn (10mm), 10 of which make a cùn (100mm).

The litre, hectare and tonne

The litre, hectare and tonne are all units that were made up to make the metric system more compatible with everyday life. These units are not part of The International System of Units (or SI, the name of the modern metric system) but are permitted for use alongside it.

There are no base units for volume in the SI as it aims to keep things as simple as possible – and seeing as volume is simply length cubed, we don’t need a separate base unit. We can use cubic metres. When the French adopted the metric system during the revolution, this cubic metre was called a stère and was used for dry quantities. But as you can imagine, this is a really large capacity for liquids (especially drinks), so they made something up that was close to the French pinte (similar to the quart in imperial) that was 10 dm³ and called it a litre. The litre survives today, although it’s not part of the ‘official’ metric system (SI).

The same goes for the hectare and the tonne, they don’t make sense in the metric system as units in themselves. The hectare is 1 hm2 (10,000 m²) and the tonne is 1 Mg (1000 kg). The separate units aren’t necessary, but endure because they sound better and are more useful to people in everyday life. What I’m proposing here is along the same lines, but more extensive.

Mesures usuelles

When the French decided to turn the country on its head via the revolution, one of the things to go was the traditional way of measuring things and time. This was really unpopular with the French people, they did not like the metric system (at first). Napoleon was the Emperor at the time and he too wasn’t a fan of the metric system. In 1812, he introduced the mesures usuelles (or “customary measures” in English) which was a compromise between the metric system and the traditional French units. In it, the traditional units were redefined using the standardised metric values as the traditional units had various definitions and sizes throughout the country at the time. For example, the livre (pound) became 500g, the tune (ell) became 120cm and the boisseau (bushel) became 12.5 litres. This, again, is along the lines of what I’m proposing here. It obviously was eventually removed, and the ‘pure’ metric system was re-instated in 1840 (they kept the litre though). Just to note also that the livre, although not a legal unit of weight any more, is commonly used in daily life today in France.


It’s not the metric system, it’s not the imperial system, it’s not the US customary system.
If we did do something like this, I guess it should have a name. Here’s some ideas:
  • The International System of Customary Units, or Customary system for short, or ‘new’ customary for short in the US. This is the official name for the metric system with the word ‘customary’ added.
  • Customary measures. Taking a leaf out of Napolean’s book with his measures usuelles. Well, more than a leaf – it’s plain plagiarism.

In summary…

You would think how we measure things would be quite simple and boring. Just a bunch of numbers and scales. But if you think about it, sometimes it actually goes a little further than that. We use units of measure in conversation, we use them in songs, we use them in poems. That’s why I believe it’s important that the everyday units we use roll of the tongue well. It’s also important that they are useful to us. Scientists, engineers, chemists etc might be perfectly happy with the ‘pure’ metric system, but maybe somebody writing a recipe, or a butcher, or Fred behind the bar, or that bloke that sells potatoes on the side of the road might be less interested in precision and more interested in units of a size that relates to ordinary people in their everyday lives.

Although the metric system is here to stay, and rightfully so; we shouldn’t just accept the inevitability of the metric system in our everyday lives. I believe the what I’ve outlined in this post would have been (or perhaps is) a good way to get the benefits of traditional, rational, units while keeping the metric system. Think of them as an ‘add on’ to the metric system.

As I said, this should be just for everyday use. All science, engineering, trade, construction or any professional areas would still use SI.

How to Hang on to your Stones!