The price per kg printed on a filament spool is a useful number, but it's not the number that matters for your wallet. What matters is the cost per gram — because prints use grams, not kilograms. A $22/kg spool and a $28/kg spool look very different on the price tag but are separated by only $0.006 per gram — less than a penny. Knowing your cost per gram lets you accurately cost individual prints, compare brands on an equal basis, and calculate material costs for customer quotes in seconds.
The formula, explained step by step
Step 1 — Cost per gram:
Cost per gram = spool price ÷ spool weight (g)
$22 ÷ 1000 g = $0.022 per gram
$28 ÷ 1000 g = $0.028 per gram
The difference is $0.006/g — on a 24 g print, that's $0.14. Insignificant for one print; meaningful across hundreds of prints.
Step 2 — Cost per kilogram (standardized comparison):
Cost per kg = cost per gram × 1000
This normalizes spools of different sizes. A 2 kg spool at $38 has a cost per gram of $0.019/g = $19/kg, cheaper than a 1 kg spool at $22/kg.
Step 3 — Cost for a specific print:
Print cost = cost per gram × grams used
$0.022/g × 24 g = $0.528
This is your material cost for this print — before electricity, labor and markup.
How to use this calculator
- Enter the spool price. Use what you actually paid, including any sales tax. If you want a true cost comparison across buying options, include shipping: divide the shipping cost by the number of spools in the order and add it to each spool's price. A $22 spool with $8 shipping from a single-spool order has a true cost of $30/kg.
- Enter the spool weight. This is the net filament weight — just the plastic, not the spool itself. A standard "1 kg spool" has 1000 g of net filament weight. The spool holder weighs an additional 200–250 g that you don't count. Check the label — it should say "Net weight: 1000 g" or similar.
- Enter the grams for this print. Slice your model in your slicer (PrusaSlicer, Cura, OrcaSlicer, Bambu Studio). The print summary shows grams. This is the material cost for one specific print.
- Read the three outputs: cost per gram (for precise quoting), cost per kg (for brand comparison), and cost for this print (your immediate answer).
Real-world examples: comparing filament value
Example 1: Budget PLA vs. premium PLA
Budget PLA: $15.99/kg → $0.016/g. For a 50 g print: $0.80.
Premium PLA+: $26.99/kg → $0.027/g. For the same 50 g print: $1.35.
Difference: $0.55 per print. If the budget PLA fails 1 in 8 prints (wasting ~25 g mid-print), the effective cost per successful print is $0.016 × (50 + 25/8) = $0.016 × 53.125 = $0.85. Still cheaper, but the gap narrows. If it fails 1 in 5 prints: effective cost ≈ $0.016 × 60 = $0.96 — almost equal to the premium option, without the consistency and surface quality.
Example 2: Single spool vs. 5-pack
Single PLA spool: $22.99 + $6.99 shipping = $29.98 effective cost → $0.030/g
5-pack PLA spools: $89.99 + $0 free shipping = $17.998/kg effective → $0.018/g
Savings per 50 g print: $0.60. If you print 100 such items per month: $60/month in savings. Annual: $720. The volume purchase pays for itself within weeks.
Example 3: Estimating costs for a custom order
A customer wants 20 copies of a 35 g figurine in PETG. Your PETG costs $0.027/g. Material cost: 20 × 35 g × $0.027 = $18.90. Add electricity (20 prints × 3 h × 0.22 kW × $0.15 = $1.98) and you have a $20.88 material + electricity cost for the entire batch. This feeds into your price calculator to set the order price.
Example 4: Exotic materials and material cost impact
Standard PLA: $0.022/g. High-speed PLA for Bambu printers: $0.034/g. PETG: $0.026/g. Polymaker CF-PA (carbon fiber Nylon): $0.085/g. The same 80 g functional bracket costs $1.76 in PETG or $6.80 in CF-PA — a 3.9× material cost difference. Knowing this upfront helps you quote the material correctly and choose the right material for the budget.
Comparing filament brands fairly
To compare filament brands on pure value, you need to account for: price per gram, failure rate, diameter tolerance, and print quality consistency. A $15/kg "brand" with 1 in 5 prints failing costs more per successful print than a $22/kg Prusament at 1 in 50 failure rate.
The simplest practical approach: buy a single spool of a new brand, track the failure rate over the first 5 prints, and calculate the effective cost per successful print. Include wasted filament from partial failures in the calculation. Only then switch your entire stock to the new brand if the numbers work out.
Specialty spool sizes
Not all spools are 1 kg. Always enter the actual net weight, not a round number:
- 250 g mini spools — common for test colors or specialties. Higher per-gram cost than 1 kg spools.
- 500 g spools — sold by some brands (Prusament Petg comes in 1 kg; some exotic materials in 500 g)
- 2 kg "mega spools" — lower per-gram cost; need a compatible spool holder (standard holders can't accommodate the diameter)
- 5 kg industrial spools — cheapest per gram; require a floor-standing spool holder and compatible extruder/Bowden setup
- Refill cardboard spools — eco-friendly option, same filament weight, but requires a reusable spool holder
Common mistakes
Using the full spool weight instead of net filament weight. A spool that weighs 1,240 g total contains 1,000 g of filament (1 kg) and ~240 g of spool. Enter 1000, not 1240. The label will say "Net weight: 1000 g" or "Filament: 1000 g."
Not including shipping in the true cost. A $16/kg spool with $9 shipping on a single-spool order has a true cost of $25/kg. Compare this to a $22/kg spool with free shipping — the free-shipping option is actually cheaper.
Comparing spools with different spool sizes. $38 for 2 kg and $22 for 1 kg — which is cheaper? $38 ÷ 2000 = $0.019/g vs. $22 ÷ 1000 = $0.022/g. The 2 kg spool is cheaper per gram. This calculator's "cost per kg" output lets you compare any spool size instantly.