What is a Calibrated Plate?

March 19, 2020 11 min read

What is a Calibrated Plate? | Kustom Kit Gym Equipment

Contents

(Updated 12/10/2021)

First off, let’s talk about some of the different types of weight plates available on the market.

BUMPER PLATES

Bumper plates tend to be used by those who enjoy high impact training such as weightlifting, undertaking movements like the clean and jerk and have also been gaining popularity amongst the CrossFit community. 

Often made from solid rubber they have a metal collar in the centre that ensures they fit on to an Olympic barbell.  Whilst they offer advantages being made of rubber this doesn’t make them unbreakable. 

Given the abuse they tend to take when being dropped overhead on to, sometimes, a solid floor more inferior bumpers can begin to crack around the collar resulting in barbell imbalance when resting on the floor. 

Bumpers are noticeable in that they are generally always the same diameter with only the thickness changing.  Popular, because they are easy to handle and, not being made of iron, they make far less noise when being dropped.
The weight accuracy of bumpers is commonly around 2 to 3% either above or below the plates stated weight and can, in more extreme cases, be as much as 10%. 

When using these plates you’d be unlikely to notice the difference unless you were utilising a large number of plates at any one time when the weight difference could begin to stack up. 

STANDARD WEIGHT PLATES

These are great for homegyms and beginners who are using less weight.  They are generally manufactured from cast iron with a 1” diameter centre hole meaning they wouldn’t fit on your Olympic barbell.

They are cheaper than most other plates and made using a cast iron mould where the finished plate is then completed with a powder coating or rubber coating. 

Unlike bumpers they vary in both diameter and thickness.  As with the bumper plates, the plate accuracy can be off by a few percent but as with bumpers this tends not to be noticeable when lifting a lower amount of weight. 

OLYMPIC WEIGHT PLATES

The most popular kind of plates for gyms, they are manufactured with a 2” diameter centre hole meaning they’ll fit Olympic bars along with most other commercial barbells and plate loaded equipment. 

They are made from a variety of different materials and available in cast iron which can be coated with either rubber or urethane.  The rubber and urethane coating tend to be more popular than bare iron as they offer extra protection against floor damage with the urethane being a better quality coating which would last longer.

CALIBRATED PLATES

Calibrated plates are typically used by those lifting significant amounts of weight in a competition environment or those in professional or elite sports environments.

There are two types of calibrated plates, those made from cast iron and those made from machined steel 

CAST IRON CALIBRATED PLATES

Cast iron plates tend to be made with a sand cast mould.  The mould, in the shape of the plate, is filled with sand and then usually has molten scrap metal poured inside.   Because of its use of scrap metal, these type of plates are much cheaper to produce. 

Cast iron plates typically have tiny pockets of air, this is due to the different kinds of metals being used and the processing of pouring molten metal into a mould.  This does mean that the plate is far less accurate than one which has been machined from solid steel. 

Once cast, the plates typically have two ‘pockets’ referred to as calibrated plugs.  The plugs are filled with lead, the lead is what helps the plate to attain its required weight and to become calibrated as lead is far denser than steel. 

However, there have been instances of the calibrated plugs working their way loose and falling out. In this instance you will be left with the tolerance of a cast iron plate, which isn't particularly accurate!

The finished plate is then powder coated, usually to the colour corresponding to its weight i.e. red to indicate 25kg or 55lbs.  The reason you are unlikely to see a cast iron plate finished with a coating such as nickel is because they have a poor surface finish.  Powder coating offers a much thicker coating that disguises these defects.  A finish such as nickel would actually highlight them and makes manufacturing them that much harder.

STEEL CALIBRATED PLATES

Machined calibrated steel plates are made using a lathe.  A lathe is a machining tool that is used to shape metal using various methods such as cutting, knurling, turning, drilling etc.

A solid steel disc is put up into a lathe.  The lathe cuts away the surface of the steel disc forming it into it's shape. They are weighed and programmes adjusted according to the density of the disc which changes with each batch of material.

As they are machined to accuracy they don’t require any additional materials to be added. 

Each plate is then finished with a coating or either zinc or nickel, this is to offer the plates a layer of protection against the elements to help with the prevention of rust. In respect of the Kustom Kit Calibrated plates, we use a nickel plating as this is a more superior coating to that of zinc. 

Steel Calibrated Plates

 

WHY ARE THEY CALLED CALIBRATED PLATES?

Some people are unsure what a calibrated plate actually means.  When something is calibrated, including a weight plate, this means it is adjusted for precision.  For example, a thermometer can be calibrated to provide a precise temperate reading.  A weight plate can be calibrated to provide a precise weight. 

When it comes to the accuracy, calibrated plates are very precise and the weight of each plate needs to come in at 0.25% or 10 grams (whichever is lighter).  This is why they are referred to as calibrated.  You may also notice that calibrated weight plates are marketed as being thinner than plates such as bumper and Olympic.

DO CALIBRATED PLATES MAKE MORE NOISE?

Thinner plates do produce more resonance during use, thus making them more noisy when compared to bumper or Olympic plates.  This noise can be further highlighted in a commercial gym environment where plates and bars are being knocked together. 

There is also a difference in noise when comparing cast iron and solid steel powerlifting plates.

Steel calibrated plates will be much more noisy during use compared to cast iron.  This is mainly due to atoms within the material.  Iron atoms in solid steel have a tightly packed structure (this is why steel plates are thinner than cast iron) and as such will rub together during impact causing a vibration.  

In the cast iron plates, these contain a far higher amount of carbon which disrupts that tightly packed structure.  This means they vibrate less which equates to less noise.  The pockets of air formed during the production of iron plates also help to reduce sound but the downside is that this makes these plates more brittle and prone to fracture during heavy impacts. 

ARE ALL CALIBRATED PLATES THE SAME?

On the face of it, they may appear the same with slight aesthetic differences but there are some factors which mean that calibrated weight plates are not all the same. 

A quick Google search and view of images will show an array of plates, many of which look virtually identical aside from their branding. 

A large proportion of these are manufactured and distributed from the same Factories in the Far East.  The only difference potentially being that of cost, with lesser known brands charging less money for the same product. 

Some manufacturers produce stainless steel plates.  These type of plates do not require any coating as they have a much higher corrosion resistance when compared to cast iron or solid steel plates.  However, this does depend on the grade of stainless steel that is being used.  It is also worth mentioning that stainless steel contains much less carbon than mild steel.  This means it has a lower yield strength making these plates more prone to denting but corrosion resistance is higher which is great for those that live near the sea!

Different brands of plates also use different finishes depending on the material they are made from. 

The most common calibrated plates are completely powder coated, usually in the colour that corresponds to its weight.  For example a 25kg / 55lb plate would be powder coated in red.  This offers two benefits. 

Firstly, it helps with identifying the weight of the plate, this is important in a competition environment

Secondly, it hides defects from the production process and prevents the plates from rusting. 

Powder coated plates tend to be the imports from the Far East all of which are made using cast iron.

The machined solid steel plates, if machined properly, have a much more pleasing appearance before any finish has been applied.  Because of this, there are more options available ranging from powder coating to zinc and nickel plating. 

A machined steel plate with a high shine, chrome like appearance is becoming more commonplace and now imported 'copies' have begun to hit the market.

However, it is worth noting that steel plates offer two different finishes.  One being zinc and the other nickel.

WHAT IS THE DIFFERENCE BETWEEN ZINC AND NICKEL PLATING?

Zinc plating is sacrificial coating that is applied to a metal surface, either iron or steel, in order to protect it from rusting. 

By sacrificial we mean exactly that, so overtime the zinc will eventually wear away exposing the metal beneath. 

Once this happens, the metal will need to be recoated.  Zinc is a lower cost finish which is not as bright and shiny as nickel so does not look as luxurious.

Zinc plating is a common finish for small hardware items such as nuts and bolts.  There are a number of calibrated plates available which are zinc plated and on first glance look similar to those that are nickel plated however zinc is a far inferior surface finish.

Zinc is likely to be the chosen finish due to it being much more cost effective.  It is worth noting that once the zinc has worn away you would have to recoat your plates to extend the life of them. 

Nickel plating is not a sacrificial coating but a decorative finish that is highly durable when compared to zinc.  This means better protection to the metal beneath, not only against wear but also corrosion.

WHY DO CALIBRATED PLATES FEEL HEAVIER THAN OTHER TYPES OF WEIGHT PLATES?

Calibrated plates, by design, offer a higher weight accuracy compared to Olympic Plates so may feel heavier. This is for one of two reasons. Firstly your calibrated plates are actually heavier than standard plates. Secondly the density is squeezed into a much smaller surface area giving the illusion of a heavier weight.

Imagine trying to pick up a tennis ball that weighed 25kg, it would be extremely difficult. 

ARE CALIBRATED PLATES HEAVIER THAN STANDARD OLYMPIC PLATES?

Calibrated plates are not harder than Olympic weight plates. 

The physical strength of the calibrated plate is dependent upon whether it has been made from either solid steel or cast from iron.

Cast iron is much more brittle than solid steel, making it a material that is far more likely to crack or split.  Whilst iron is a very hard metal is does break easily compared to steel which carries a higher tensile strength, meaning it can withstand higher stresses than that or iron.

WHY ARE CALIBRATED PLATES DIFFERENT COLOURS?

Calibrated Plates are different colours to help with the identification of its weight.  This is important in a competition environment when a powerlifter has a barbell loaded with plates, it is then easy for the three referees to calculate the weight on the bar.   The colours are as follows:

  • 25kg plate / 55lb plate – Red plate
  • 20kg plate/ 44lb plate – Blue plate
  • 15kg plate / 33lb plate – Yellow plate
  • 10kg plate / 22lb plate – Green plate
  • 5kg plate / 11lb plate – White plate
  • 2.5kg plate / 5.5lb plate – Black plate

Whilst we have referenced lbs above it is important to note that currently calibrated competition plates are only available in kgs. 

Whilst most, if not all, cast iron calibrated plates are powder coated, the steel plates that are produced by us at Kustom Kit feature a groove which is machined around the diameter of the plate, this is painted with its corresponding colour.  Some steel plates offer no colour coding so these would be unsuitable for a competition environment. 

WHERE DO THE BENEFITS OF CALIBRATED PLATES COME IN?

As an example, if you’re simply loading a 25kg bumper plate on each side of your barbell you wouldn’t necessarily notice any weight imbalance when squatting, benching or deadlifting.  However, if you load four 25kg plates on each side you’d expect to be lifting 200kg (excluding the bar and collars).  The reality though is there could be a significant difference:

Based on a 3% accuracy of each 25kg bumper plate, the total weight could vary between 194kg and 206kg, split unevenly across your barbell.

As a worst case scenario, based on 10% accuracy of each 25kg bumper plate, the weight difference could be as much as 180kg to 220kg, again split unevenly across your barbell.

This would be very noticeable when lifting! Essentially, accuracy becomes more important with the more you lift. 

If you load 200kg of calibrated plates on your barbell, then you’re lifting 200kg pretty much on point.  

When it comes to the thickness of the plate, the advantages are again noted by those who lift large amounts of weight. 

When the plates are thinner it enables the user to load more plates on to their barbell and keeps the weight nearer to the centre of the bar.  This is beneficial for squatting and deadlifting as keeping the weight close to the centre means less bend on the bar and less whip.  Less whip means that the user remains more stable, thus making it safer. 

When it comes to whether or not calibrated plates are worth it.  Consider the kind of gym members you have and how they lift.  If many lift big numbers then calibrated plates could be a worthwhile investment.

HOW DID THE USE OF CALIBRATED PLATES COME ABOUT?

As we know, calibrated plates tend to be favoured by the powerlifting community, primarily due to the extreme amount of weight being lifted and the requirement for accuracy of that weight on the lifter’s barbell. 

The sport of powerlifting itself did not become mainstream until the 1950’s where it derived from ‘odd lifts’.  Odd lift competitions comprised of a great many exercises with each exercise having a ‘three attempt’ format.  You can read more about the history of strength sports here.

Bob Hoffman of the York Barbell Company hosted and funded the first unofficial World Championship for powerlifting in 1971.  Only two countries took part, the USA and the UK.  Other countries seemed reluctant to compete due to the inconsistencies with the regulations and the format of the competition.  

In 1972, keen to standardise the rules and encourage better participation, representatives from competing countries came together and formed the International Powerlifting Federation.  Despite regular regional, national and international competitions it wasn’t until the mid 1980’s that calibrated plates were used in a competition environment.

This is because it had become apparent that there were irregularities with what the competitors had been lifting. 

In 1975, Don Reinhoudt had set a world record squat, bench and deadlift total of 1098kg / 2420lbs.  However, this was later downgraded to 1084.5kg / 2391lbs.  Upon weighing the equipment used there was an inconsistency of 13.5kg / 29.7lb, meaning that either the plates or barbell were not accurate in respect of weight.

In 1982, Mike Bridges competed in his class setting a combined lifting total of 901.8kg / 1984lbs.  This was later upgraded to the correct total 308.8kg / 1999lbs.

The above examples highlighted that the inconsistences could have a huge impact on a lifters combined total, potentially making a difference between winning and losing a competition and indeed setting a world record. 

This is why today, the IPF have strict rules with equipment that can be used at their competitions with all equipment having to be either IPF specification (for national and regional competitions) and IPF approved for the international level competitions.  


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