Key Factors in Calculating Injection Mold Costs

Author - Tom Wood, Senior Vice President Sales

Quoting an injection molded plastic part involves more than just crunching numbers—it’s about understanding all the elements that impact the final injection mold price. Accurately quoting injection molded plastic parts ensures you cover all production costs while remaining competitive in the market. It helps prevent profit loss from underestimated expenses and avoids overpricing that could drive customers away. A precise quote also builds trust with customers by setting clear expectations from the start.

An accurate quote starts with a well-prepared customer Request for Quote (RFQ). Let’s walk through the core components that make up a quote:

Key Cost Drivers in Injection Molding

Part Weight - To calculate part weight, start with the part’s size and material density (specific gravity). This data usually comes from the part’s 3D model or 2D drawing. If it’s a physical sample, you can weigh it using a gram scale. You’ll also want to consider the runner weight (excess material used during molding). A good rule is to calculate part weight in grams × 2.2 to get pounds per 1,000 parts.

Material Price - If the customer has contracted pricing directly with a resin supplier, verify that the cost per pound matches your expected order volume. If not, you’ll need to source the material yourself—check with distributors and request up-to-date pricing.

Press Size – Identify the appropriate press size by determining the approximate square inches of the part (length × width × depth). Multiply that by 2.5 to get a rough estimate of the required tonnage for your injection molding press. For example, a 100-square-inch part would typically run in a 250-ton press.

Press Rate Per Hour - Press rates vary by press size, industry, and location. For instance, medical-grade molding typically has higher rates than general industrial work. Industry associations like MAPP (Manufacturers Association of Plastic Processors) offer regional press rate data to guide your estimates.

Setup Costs - Setting up the mold in the press involves connecting water, hydraulic lines, wiring, and configuring hot runners or lifters. Some molders use flat-rate setup charges based on press size, while others calculate based on actual setup time. These costs are usually amortized over the production run.

Efficiency & Scrap Rate - Here’s where you evaluate your expected production efficiency. Most tools run at around 95% efficiency, with 3% scrap being fairly normal. If the part includes inserts or components, consider whether defective parts can be reprocessed or if they must be scrapped entirely.

Packaging - Packaging needs to protect the part during transit without being excessive. We recently started a pilot program using stackable vacuum-formed skids which are very cost-effective for lightweight parts. Understanding your customer's packaging expectations—and whether they'll share costs—is a key part of quoting.

Inserts / Purchased Parts - If the part requires inserts or external components, list those costs clearly in your quote. With volatility in today’s supply chain, it is important to share these costs with you customer as part of your quote.  Adding a reasonable markup is common, but you can also let customers supply them directly to avoid additional margin.

Decorating / Assembly - Any secondary operations—like pad printing, ultrasonic welding, or assembly—should be quoted separately or integrated into your per-part cost.

Miscellaneous Costs - Don’t forget to account for: Sales commissions, tooling maintenance, engineering time (NRE), end-of-arm tooling and workstation investments. In some cases, a customer’s appetite for any of the above is unwelcome at face value so amortizing these costs into your quote is another way to accomplish getting compensation.

Markup Over Cost - Finally, apply your target markup percentage to ensure acceptable profit margins. This mark-up is your best attempt and estimate to make sure that part generates an acceptable net profit. With an ERP system, you can track which parts meet margin targets and which fall short.

Quoting isn’t just a pricing exercise—it’s a process that balances accuracy, transparency, and profitability. Using quoting software or tools that incorporate all of these elements ensures: Faster quote generation, consistent, data-driven pricing and, ultimately, better decision-making with clear metrics.