Injection Molding Cost Calculator — Per Piece, Mold Amortized
Who this is for: For product developers deciding whether 10k units justify a mold — and for shops quoting production runs where 'the mold is $15k' needs to become a per-piece number.
Part weight, cycle time, cavities and mold cost in — get the per-piece price split into resin, machine and mold amortization.
Quick answer: Per-piece = part weight × resin + (cycle ÷ 3600 × press rate ÷ cavities) + (mold ÷ life shots). Example: 25 g PP, 30 s cycle, 4 cavities, $45/h press, $15k mold over 100k shots = $0.034 + $0.094 + $0.15 = $0.28 per piece. Volume turns tooling from a wall into a rounding error.
g
$/kg
s
Cooling is 60–80% — walls²
$/h
$
shots
Per piece
$0.281
4 cavities, 30 s cycle
Mold amortization
$0.1500
$15,000 ÷ 100,000
Machine per piece
$0.0938
÷ 4 cavities
Resin$0.0375
Machine time$0.0938
Mold amortization$0.1500
Per piece$0.2813
At a 10,000-piece run the mold adds $1.50/piece; at 100k it's $0.150. Volume turns the mountain into a rounding error — but design changes reset the counter. Freeze the design first.
Per piece = resin + (cycle ÷ 3600 × press ÷ cavities) + (mold ÷ life shots). Resin: PP $1.2–1.8 · ABS $1.8–2.5 · PC $2.5–4 /kg. Presses: $35–65/h for 100–300 T (US 2026).
Core facts
Resin
PP $1.2–1.8 · ABS $1.8–2.5 · PC $2.5–4 /kg
Press rate
100–300 T: $35–65/h (US 2026)
Cycle driver
Wall thickness — cooling is 60–80%
Example
25 g PP · 30 s · 4 cav · $15k/100k = $0.28
Rule
IM wins above ~5–10k units
Status
Quotes use standard shop math: machine-hour rate × cycle time + materials + setup amortization. SFM/chipload figures are conservative HSS starting points (carbide runs 3–4× SFM). Compiled September 2026 — estimates for budgeting; real quotes come from the shop that runs the job.
How is injection molding priced?
Three streams. Resin: part weight × resin price (ABS $1.8–2.5/kg, PP $1.2–1.8, PC $2.5–4) — a 25 g part is pennies of plastic. Machine: cycle time × machine rate ÷ cavities — a 30-second cycle on a $45/hour press is $0.375 per shot; a 4-cavity mold splits it to $0.094 per part. Mold amortization: mold cost ÷ lifetime shots — a $15,000 four-cavity tool at 500k shots adds $0.0075/part, but at a 10,000-piece run it's $0.375. Example: 25 g PP part, 30 s cycle, 4 cavities, $45/h press, $15k mold over 100k shots: $0.034 resin + $0.094 machine + $0.15 mold = $0.28 per piece — which is why injection molding only makes sense above a few thousand units.
Common uses
Deciding the break-even volume vs 3D printing or CNC
Quoting a production run with mold amortization shown separately
Comparing cavity counts (2-up vs 4-up mold) on per-piece price
Budgeting resin choices (PP vs ABS vs glass-filled) at volume
Frequently Asked Questions
How much does injection molding cost per part?
At production volume, pennies: a typical 20–30 g consumer part runs $0.10–0.50 including amortized mold at scale. The mold itself is the big number — $3k–15k for simple single-cavity tools, $20k–80k+ for multi-cavity or complex parts.
How is the mold cost amortized?
Mold cost ÷ lifetime shots, added to each piece. Quote honestly: a $15k mold over a 10k-piece run adds $1.50/part; over 500k shots it's $0.03. If the customer's volume is uncertain, quote mold as a separate line (tooling fee) instead of baking it into the piece price.
What does cycle time depend on?
Wall thickness dominates — cooling is 60–80% of the cycle, and it scales with the square of wall. A 2 mm wall might run 20–30 s; 4 mm doubles or triples it. Rib your parts thin or pay per second forever.
How many cavities should my mold have?
Cavities split the machine time: 4 cavities at the same cycle = quarter the machine cost per piece, at roughly 2–2.5× the mold cost. Break-even usually lands at 10k+ pieces per year of demand. The calculator shows both numbers.
What machine rate should I use?
$35–65/hour for 100–300 ton presses is the 2026 US band; China ranges $15–35. Bigger tonnage (thicker parts, bigger projected area) climbs the scale. The resin supplier's datasheet and the molder's press list decide the real number.