SpoolPilot · Resources

How to track filament inventory for a 3D printing business

By an Etsy seller with 3,000+ sales

Count sealed spools by scanning the barcode when they arrive, treat an opened spool as in use, and get weeks of stock from how fast your sales consume each material. Unlike weighing every spool, this keeps working through a busy week, and it answers the two questions a business has: can I fill this week’s orders, and when do I reorder?

By Sean, who runs Opus Design Company on Etsy: five years, 3,000+ sales. Last revised October 2, 2026.

The two questions inventory has to answer

A hobbyist wants to know how many grams are left on the spool, because the next print has to fit. A business wants to know two different things: is there enough of this material for the orders coming in, and when do I need to order more so it arrives before I run out. Both are questions about pace, not weight. A spool with 400 g left is plenty for a product that sells twice a month and a crisis for one that sells daily.

How do you count filament spools?

Count sealed spools, not grams. The sealed spool is the unit of business inventory: it is discrete, it has a barcode, and its contents are known exactly. Scan the barcode when a box arrives and the count goes up by the number of spools; scan when you open one and it moves from “on the shelf” to “in use.” Five seconds per box, and the count is right. When a material is down to one sealed spool and the open one, you know without walking to the shelf.

Restock day is where counting by barcode earns its keep. A case of the same spool arrives, you scan one, then tap plus for each of the rest or type the quantity if it is fifty. SpoolPilot works this way, and it also builds a shared library of scanned barcodes so a spool you have never bought before is recognized the second time anyone in the app scans it.

Should you weigh open spools?

Not as a habit. Weighing an open spool works once, and it fails as a routine. Subtract the empty-spool weight, write the number down, repeat after every print. Most people do it for two weeks.

The version that lasts is derived remaining: you know the spool started at 1,000 g and you know the grams of each print that came off it (the slicer told you), so remaining is a subtraction you never have to do by hand. Derived remaining drifts a little with purge and failed starts. For a business that is fine; the sealed count behind it is exact, and the open spool is one of many.

Precision matters in one case: a single large print that needs most of a spool. Weigh for that one, then go back to counting.

How do you know how much filament you’ll use?

From your sales. If a product uses 47 g of a material and sold 30 units last month, that product alone consumed 1.4 kg of it. Add the other products that use the same material, then add what failures and prototypes ate, and you have a monthly usage rate per material. That usage rate is the number a spreadsheet of spool weights cannot give you, because it lives in your sales history, not on the shelf.

When should you reorder filament?

Reorder when a material’s weeks of stock drops to the supplier’s delivery time plus the safety margin you want.

weeks of stock = (sealed spools × spool weight + estimated remaining on open spools) ÷ weekly usage.

Example: three sealed 1 kg spools of a black PLA, about 400 g left on the open one, and products that use 800 g of it a week. (3,000 + 400) ÷ 800 = 4.25 weeks. If the supplier takes a week to deliver and you want a week of safety, reorder when the number hits two. The same material in a color that sells slowly might show 40 weeks, which tells you not to buy more of it, however good the sale price is.

Failed and unsold prints

Inventory only reconciles if everything that consumed filament is counted, and the things that consume it without producing a sale are the ones that get skipped: the failed print, the test cube, the prototype, the stock you printed ahead of a season that has not sold yet. Log them. A “scratch print” entry that just says 40 g of the gold went to a failed test keeps the usage rate honest, and when the shelf is empty a week early you will know why. The failure log is also where the pricing failure-rate multiplier comes from; the pricing page shows how it changes a price.

Why isn’t weight alone enough?

Because grams remaining is a fact about one spool, and weeks of stock is a fact about your business. The first tells you whether the next print will finish; the second tells you whether to place an order today, whether a new product’s material is one you can commit to, and whether the bulk discount on a slow color saves money or ties it up on a shelf. A filament tracker built for hobbyists optimizes for the first question and is very good at it. A shop needs the second, and the second needs sales data.

Common mistakes

• Weighing rituals that collapse by week three, leaving worse data than a simple count.
• Counting open spools as full, or not counting them at all.
• One usage rate for “PLA” when the black sells five times faster than the teal.
• Reordering on gut and discovering the popular color is out the week before a holiday.
• Not logging failures, so the shelf and the spreadsheet disagree and nobody trusts either.
• Buying the bulk deal on a material that shows forty weeks of stock.

Spreadsheet, filament tracker, or something else

A spreadsheet with one row per material, a sealed count, an estimated open amount, and a weekly usage number you update monthly is a workable system for a small shop, and better than most. The sheet breaks on the usage number, which has to be recomputed from sales by hand, and on the scanning, which a sheet cannot do.

Dedicated filament trackers such as Spoolman are excellent at grams remaining, printer integration (it updates spool weight as a print runs through Klipper’s Moonraker or OctoPrint), and QR labels for each spool, and have no idea what you sold. If material precision is your problem, they are the right tool; Spoolman vs SpoolPilot compares the two side by side.

SpoolPilot does the business version: sealed spools counted by barcode scan, weeks of stock computed from your real sales pace per material, a print-next queue ranked by how soon each product runs out, and a low-stock warning that stays quiet for materials you don’t sell through. Filament inventory is part of the free tier with no limit; the forecasts are part of Pro. Where it sits next to the rest of a shop’s numbers, and how to decide between these options, is in what software a 3D printing business needs.

More: Spoolman vs SpoolPilot · how to price your prints · real profit on a print · what software a 3D printing business needs