Count the Turns

…of filament on the spool to know how much filament remains.

I guess a lot of people hate wasting the last little bit of filament on a spool as I do. But it is not super convenient to remove the spool from the machine to measure it just to determine you have 50g remaining. So here is a super effective and easy way to know how much filament is remaining based on how many turns of filament you can count on the spool.

Multiply the number of turns of filament remaining on the spool by the mass of one turn of filament. Let’s say one turn of filament is 1g, and you have 15 turns remaining, then you have 15g of filament remaining. Bamm! Superfast.

I recently started using this simple technique and it has helped me immensely in time saving and filament-not-wasting. I am going to explain the entire process here but you do not need to know it. You just need the spreadsheet or the tables I will provide and you can print it, keep it near your printer, and reference it anytime. No more throwing away the last bit of filament.

So the only thing you need to know is the mass of one turn of filament. And, this is easy to know and it will remain relatively constant. The mass of one turn of filament is based on its length… the inner diameter of the spool (it doesn’t change too much), the diameter of your filament (generally 1.75mm or 2.85mm), and the density of the filament material (I will give you those below). And, since most of those will be constant to the few types of filaments and spools you use, you can keep the results handy and estimate the amount of filament remaining very quickly and very accurately. Voila!

The quick reference table above gives you the values you might need for typical circumstances but you can adjust them to suit your needs in the spreadsheet. I emphasize downloading the spreadsheet because if you edit the shared version online it will be constantly changing as others might be editing it too. So download it and make it yours.

The process

This technique is suitable when you can see the inner core of the spool. Count how many turns of filament are on the spool. Then you have two choices…

Option A: Calculate – using the spreadsheet I have linked below, enter the size of your filament, the spool diameter, and the type of filament along with the number of turns you counted and the total remaining filament will be calculated.

Option B: Quick Reference – Referring to the Quick Reference table in the spreadsheet (and shown earlier above), multiply the number of turns by the grams per 1 turn of filament. The result is the total remaining filament on the spool.

Option C: Estimate – It turns out most 1kg spools have an inner core of around 90mm. And, most filaments have a density of about 1.1g/cm3. So generally speaking you have about 0.75g per turn. You can be more accurate if you are always using one or two types of materials and use the appropriate density for it from the quick reference table. But on 1kg spools, multiply the number of turns remaining by 0.75 and the result is a good estimate of how much material remains. For example, 10 turns = 7.5g of material. It is a little more for PLA and PETG and a little less for ABS and ASA for example.

The Math

The inner diameter of the spool tells us what the length of each turn is (1 turn length = circumference = 2*pi*r), and we can calculate the volume of material based on that and the crossectional area of the filament (volume = (pi*r2) x ( 2*pi*r)). Once we have the volume we just need to multiply it by the density.

The math itself is simple and assumes you are near the inner core of the spool. If you tried to count the number of turns to an entire layer and then multiply that by the number of layers of filament remaining you would get a decent estimate but increasingly inaccurate the more there is remaining on the spool. The good news is there would be more than you calculate so you would be on the safe side.

However, all of the calculations depend on the material densities in the Material Densities table below (and in the spreadsheet). Feel free to adjust those to suit your specific filaments as desired.

In my case, I have made a note of the few spool sizes and filaments I use and can do the math super fast in my head accurately enough to know if it is safe to print or not or even how much printing time I have before the spool is empty.

I won’t throw out any numbers for how long a gram of filament takes to print because it will vary based on everyone’s individual machine and setup. But you can easily see it when you slice your next print. Take a note and figure out the average over a few prints. This will give you a number and you can then know that if you have x amount of filament remaining, you will run out in n minutes and set an alarm on your phone to head back to the printer at that time and attend to the filament change.

You can find the spreadsheet here…

https://docs.google.com/spreadsheets/d/1dObC2LBqF5k6Q6eR7UHsD5cj8fTOo_wXjnk8IAvaw9g/edit?usp=sharing

I welcome all comments and feedback.