Guide · 5 min read · Updated
Plate Loading Math: How to Load a Barbell
Loading a barbell is one subtraction and one division: take the bar weight off the target, halve what is left, and put that amount on each side using the heaviest plates first. For 100 kg on a 20 kg bar, (100 − 20) / 2 = 40 kg per side, which is a 25 kg plate and a 15 kg plate. If you use weighted collars, subtract those too before you halve. The plate calculator does the sum for any bar, any unit and the plates you actually own.
The formula
Per side = (target − bar − both collars) / 2
Then build the per-side number from your plate set, largest first. Three worked examples in kg, all on a 20 kg bar with spring clips (which weigh so little they are ignored):
| Target | Per side | Plates per side |
|---|---|---|
| 60 kg | 20 kg | 20 |
| 100 kg | 40 kg | 25 + 15 |
| 142.5 kg | 61.25 kg | 25 + 25 + 10 + 1.25 |
And three in lb on a 45 lb bar:
| Target | Per side | Plates per side |
|---|---|---|
| 135 lb | 45 lb | 45 |
| 225 lb | 90 lb | 45 + 45 |
| 315 lb | 135 lb | 45 + 45 + 45 |
The lb examples explain why 135, 225 and 315 are the landmark numbers in lb gyms: each is one more pair of 45s on a 45 lb bar.
Bar weights
The bar is the part people forget to count, and it varies more than plates do:
- Men’s Olympic bar: 20 kg (44 lb). Also the common “45 lb bar” in lb gyms, which is 20.4 kg.
- Women’s Olympic bar: 15 kg (33 lb), thinner shaft and shorter.
- Technique or training bars: often 5, 10 or 15 kg; some are aluminium and light enough that the weight is printed on the end.
- Specialty bars: safety squat bars, trap bars and multi-grip bars range from about 20 to 35 kg. Weigh or look up the one in your gym.
- Fixed barbells and smaller “standard” bars: anywhere from 5 to 15 kg.
If you train in more than one gym, write the bar weight in your log along with the gym. A 100 kg squat on a 20 kg bar and a 100 kg squat on an unmarked 17 kg bar are not the same lift. The guide to using a lifting log covers what else belongs on the page.
Collars
Spring clips weigh a few hundred grams a pair and are normally ignored. Competition collars are a different matter: in weightlifting and powerlifting they weigh 2.5 kg each, so a loaded bar with collars carries an extra 5 kg. The IWF and IPF rule books specify the bar, collars and plate set used in competition, and gyms with competition-style equipment follow them. If you lift with weighted collars, subtract 5 kg (or whatever yours weigh as a pair) before you halve. The plate calculator has a collars field for exactly this.
Plate weights and colours
Competition kg plates follow a fixed colour code that many gym bumpers copy:
| Plate | Colour |
|---|---|
| 25 kg | red |
| 20 kg | blue |
| 15 kg | yellow |
| 10 kg | green |
| 5 kg | white |
| 2.5 kg | red (small) |
| 1.25 kg | chrome or black (powerlifting) |
Weightlifting change plates continue the sequence in smaller sizes (2 kg blue, 1.5 kg yellow, 1 kg green, 0.5 kg white). Iron gym plates are usually black or grey regardless of weight, so read the number, not the colour.
Common lb plates are 45, 35, 25, 10, 5 and 2.5 lb, with 1.25 lb and 55 lb plates less common. A “45” weighs 20.4 kg; a 20 kg plate weighs 44.1 lb. They are close enough that some gyms mix them, which is where mistakes come from.
Converting between kg and lb
1 kg = 2.2046 lb, and 1 lb = 0.4536 kg. Two mental shortcuts:
- kg to lb: double it, then add 10 percent. 100 kg → 200 + 20 = 220 lb (true value 220.5).
- lb to kg: halve it, then take off 10 percent of that. 225 lb → 112.5 − 11.25 ≈ 101 kg (true value 102.1).
For exact work, use the calculator rather than the shortcut; the plate calculator converts and then rounds to a loadable weight in the unit you choose. When you switch units in the lifting log generator, it converts your entered sets and rounds to the nearest 2.5 kg or 5 lb.
Loading order and small plates
Heaviest plates go on first, closest to the shoulder of the bar, with the smaller plates outside them and the collar last. This keeps the load stable and makes the bar read the same from either end.
Small plates matter more than their size suggests. Progression on upper-body lifts often needs 1 or 1.25 kg jumps (2.5 lb in lb gyms), and the ACSM’s guidance of raising load by about 2 to 10 percent when reps are met is impossible on a 40 kg press with nothing smaller than a 2.5 kg plate, because that is already a 12.5 percent jump. If your gym has no fractional plates, a pair of 0.5 or 1.25 kg plates in your bag solves it. The guide to how much weight to add each week explains why the increments differ by lift.
When the exact weight cannot be made
Sometimes the per-side number is not loadable: 101 kg on a 20 kg bar needs 40.5 kg a side, which needs a 0.5 kg plate. You have three options:
- Round down to the nearest loadable weight (100 kg) and do the prescribed reps.
- Round up (102.5 kg) if the plan was on the light side anyway.
- Add a little with a fractional plate or a magnetic microplate.
Programs built with percentages produce odd numbers constantly, which is why the log generator rounds every target to a chosen increment before printing. Tick only the plates you own in the plate calculator and it will show the closest load it can make and the gap.
Warming up with the same arithmetic
A warm-up ramp is just this sum repeated at each step. For a 100 kg work set: 20 (bar), 40 (a 10 a side), 60 (a 20 a side), 80 (a 20 and a 10 a side), then 100 (25 + 15). Working this out once before the session and writing it on the log saves the between-set mental maths. The guide to warm-up sets shows how to choose the steps.
Questions lifters ask
How do I work out which plates to put on the bar?
Subtract the bar weight from the target, subtract both collars if you use weighted ones, then divide by two. That is the load per side. Build it from the heaviest plate down: for 100 kg on a 20 kg bar, (100 − 20) / 2 = 40 kg per side, which is a 25 and a 15.
How much does a barbell weigh?
A standard men's Olympic bar weighs 20 kg (44 lb) and a women's bar 15 kg (33 lb). In lb gyms the standard bar is 45 lb (about 20.4 kg). Technique bars, trap bars and specialty bars vary, so check the bar before you count on it.
What do the plate colours mean?
On competition kg plates the colours are standard: 25 kg red, 20 kg blue, 15 kg yellow, 10 kg green and 5 kg white. Smaller change plates repeat the sequence. Many gym bumpers follow the same code, but iron plates are usually black or grey, so read the number.
Is 100 kg the same as 220 lb?
Close: 100 kg is 220.5 lb, and 1 kg is 2.2046 lb exactly to four places. In a lb gym the nearest loadable weight is usually 220 lb (45 lb bar plus two 45s, a 25, a 10 and a 2.5 per side).
Sources
- International Weightlifting Federation. Technical and Competition Rules & Regulations . IWF, current edition
- International Powerlifting Federation. Technical Rules Book . IPF, current edition
- American College of Sports Medicine. American College of Sports Medicine position stand. Progression models in resistance training for healthy adults . Medicine & Science in Sports & Exercise, 2009;41(3):687-708
This guide is general education about training, not medical advice. If something hurts, stop and get it checked by a qualified professional.