T Nation

My Weight / Rep Calculator


Don't know if anyone is interested or not, but I got bored this afternoon and wrote a simple calculator to figure out your 1RM etc. when you input how much you lifted and how many reps on a given lift.

The percentages I used are based on my own experiments. So it's not perfect science, but it works for me. I'm doing Waterbury's TBT right now and I wrote this to help me figure out how to adjust the weights with each workout as the reps change.

A zip file can be downloaded here:


Just unzip the two files (exe and dll) into a folder together.

Here's a screenshot of what it looks like:


That's great and all, but it takes the fun out of actually finding out your max on each exercise and then figuring the percentages, ya know?


I can see that but what I use it for is outside of working on my 1RM. Like if I start TBT and Monday I'm squatting 3 x 5 at 160 (sucks I know, but I haven't been lifting long). Then on Wednesday I'm going to be squatting 3 x 8 (and Friday 2 x 15). I use this to figure out how much I'd use for those days.


This is cool!




Cool! Are you into comp.science? I love making these type of things. What formulas did you use?


Great job!

But as i can increase the weight with 2,5 kg, it would be nice with an option that rounded down with the interval 2,5.

I am a programmer too, but haven't done any programming lately.


I'm an IT Director for a medium-sized city in South Louisiana, but programming has always been a hobby of mine.

As for the formulas:
I have an array that has the percentages for the weight each # of reps would be. For instance, 1RM = 100%, 5RM = 86%, 8RM = 78%.

Once you put in the weight you lifted and the number of reps, I grab the percentage that is at the index in the array that matches the number of reps. Then it divides the weight you lifted by that percentage to get the estimated 1RM.

So if you put in that you lifted 80 for 5 reps. It divides 80 by .86 to give you an estimated 1RM of 93.

After that it cycles through the array and multiplies the 1RM weight by the percentages at each index.

For increasing weight with each workout, I went with 1.25% - 2.5% since I've seen CW recommend those percentages. After it calculates what you should lift in your next workout based on which weight increase percentage you selected.

Like I said, it's not perfect. For instance, earlier today I read where CW estimated that your 18RM would be about 60% of your 1RM, but I have it at 56%. But it works for me and I don't think it'll make a huge deal.


The weight increases aren't in kg but percentage of the weight you lifted. I left the program ambiguous enough so that you can calculate lbs or kgs.


No shit? Where, Lafayette, Houma, Lake Charles, or Morgan City?


Morgan City. It's the perfect job for keeping my training schedule on track. 35 hours / week is fulltime, no weekends, and off at 4 every day.


Sweet man. That's a great schedule. I'm a lab tech for a refrigerants plant in Geismar on the Miss. river. 12hour rotating shift for me. Hence me at work now.


hey jd_dd

great stuff-thanx but iam not able to download the file.

Regarding to the programm TBT-I don?t get the sense of the progression.
Every week consists of different paramters.

On any other programms you have different paramters throughout the week-and the next week the paramters are still the same.
Fex 4x10 5x5 10x3
So next week I try to do on monday 4x11 fex.
On the TBT its the other way around:
2x15 3x5 2x10
next week:
2x20 3x8 2x18

How can I improve the weight then?
Before the TBT I calculate my rep maxima and then write down my weigths for the following 8 weeks-but isn?t that wrong? The weigtht calculated in week 5 fex.is still orientated on the 1rpm BEFORE the cycle-but I will get stronger in the cycle-so I have new 1rpms from week to week...
can somebody help me out?


i think it?s pretty cool what ya did there with this calculator!
just one thing, though: the curve of your percentages is not linear but logarithmical. the top of the curve is about a line but at the bottom are great differences! therefore is e.g. 90% of your 100kg 1RM max not 90kg but ca. 95.4kg and 50% are 69.9kg.

i got a table at home with the values, but i don?t know if i?m allowed to post them since i got them from my prof. at univerity and it?s copyright. i?m just gonna name some here:

percentage - tablevalue
95% - 0.977
90% - 0.954
85% - 0.929
80% - 0.903
75% - 0.875
70% - 0.845
65% - 0.812
60% - 0.778
55% - 0.740
50% - 0.699
40% - 0.602
30% - 0.477

these values are not 100% exact for they vary especially from fast twich dominant to slow twich dominant persons, but they are nearer to the truth than the linear values.
what i want to say is, that if you take your 5RM (which is as you said about = 85% of your 1RM) to get to your 1RM, your won?t get the right 1RM like this:

(a : 85) x 100 a = 5RM max

but rather like this:

(a : 93) x 100

hope i could help you a little bit to make your little calculator even cooler!


Thanks, man! Anything I can do to improve it is welcome. The percentages I had were just estimates on my part. I knew they would be off, but I didn't realize they were that far off. I'm going to recompile it with the percentages you listed above and rehost it.


I corrected my code using the percentages da sheep posted (thanks again). That only gave me a range of 1 - 15 reps but I'd rather not have the higher rep range with bad percentages.

Here's a link for the new download:


Hey the program just stopped working for me.

RepCalc.exe - Programfejl

Det lykkedes ikke at initialisere programmet korrekt (0xc0000135). Klik p? OK for at afslutte programmet.


This error. I tried downloading it again, but same error:S


the same happens to me. :frowning: