What file format should I send for a 3D printing quote?

Send a STEP (.step or .stp) file when you can — it preserves exact geometry, units, and editable surfaces, which lets the provider check manufacturability and adjust the part. Send an STL only if STEP is unavailable; an STL is a fixed mesh that can't be easily modified and is more prone to errors. If you have both, send both. Avoid sending only a native CAD file (like SolidWorks or Fusion) unless asked, since not every provider can open it.

What information do I need to include to get an accurate 3D printing quote?

Include the quantity, the material or material family you want, the units your file uses (mm or inches), any critical tolerances or features, the intended use of the part, and your target turnaround. A provider can quote a clean file with this brief in minutes; a file with no context forces a round of questions and delays the price.

Why does my 3D printing file need to be watertight?

A watertight (manifold) mesh has no holes, gaps, or flipped faces, so the printer's software can clearly tell what is inside the part versus outside. Non-watertight STL files cause failed slicing, missing walls, or rejected quotes. Most CAD tools export watertight meshes automatically; free repair tools like Microsoft 3D Builder or the Autodesk mesh repair service can fix a broken one.

What units should my 3D print file be in?

Always confirm units before sending. STL files do not store units, so a part modeled in inches can import as millimeters and print 25.4 times too small. State the units in your message (for example 'dimensions in mm') and, ideally, give one known overall dimension the provider can verify against, such as 'overall length should be 80mm.'

How can I lower the cost of my 3D printing quote?

Send a clean STEP file with a clear brief so the provider spends no time chasing details. Hollow large solid parts where strength allows, reduce unnecessary volume, batch multiple parts into one order so they nest in a single build, and avoid over-specifying tolerances you don't actually need. Each of these directly reduces material, labor, or setup cost.

How to Prepare Your Files for a 3D Printing Quote (Faster, Cheaper, Right the First Time)

The difference between a 3D printing quote that comes back in an hour and one that drags on for three days of back-and-forth is almost never the part — it's the file and the brief. A clean file with a clear one-paragraph description lets a provider price your job immediately. A vague request with a questionable file triggers a round of clarifying emails, slows everyone down, and often produces a higher quote to cover the uncertainty.

This guide walks through exactly how to prepare your files and brief so you get a faster, cheaper, and more accurate quote — and a part that comes out right the first time.

Send the Right File Format

Format is the first thing a provider looks at, and it sets the tone for the whole quote.

STEP (.step / .stp) — preferred. A STEP file stores exact, editable geometry and (usually) units. Providers can inspect it for manufacturability, adjust wall thicknesses, and re-orient features. This is the format that gets you the best quote.
STL — acceptable, with care. An STL is a fixed triangle mesh. It works, but it can't be easily modified, it stores no units, and it's the most common source of errors. Send STL only when STEP isn't available — and if you can, send both.
Native CAD (SolidWorks, Fusion, Inventor) — only if asked. Not every bureau can open your specific CAD package. Don't assume; export a neutral format.

If you're unsure which to use or why STEP beats STL for manufacturing, our explainer on STL vs. STEP files breaks down the trade-offs in plain language.

Make Sure the Mesh Is Clean

A file that opens isn't necessarily a file that prints. Two problems sink more quotes than any other:

Not watertight. The mesh must be manifold — no holes, gaps, or flipped faces — so the slicer can tell inside from outside. Most CAD exports are watertight by default; if yours isn't, free tools like Microsoft 3D Builder will repair it in a couple of clicks.
Wrong resolution. An STL exported too coarsely shows visible facets on curved surfaces; exported too finely, the file balloons to hundreds of megabytes for no benefit. Aim for a chord tolerance around 0.01–0.05mm — smooth curves without an enormous file.

Get the Units Right (The 25.4x Mistake)

This is the single most common — and most expensive — file error. STL files do not store units. A part modeled in inches can import into the provider's software as millimeters and come out 25.4 times too small (or too large). To prevent it:

State the units explicitly in your message: "all dimensions in mm."
Give one known overall dimension as a sanity check: "overall length should be 80mm."
When possible, send STEP, which carries units far more reliably than STL.

One sentence here saves a scrapped print and a wasted lead time.

Write the One-Paragraph Brief

The brief is what turns a file into a quote. Include these six things and a provider can usually price the job the same day:

Quantity — one part, ten, or a hundred. Quantity changes both process and per-part price.
Material (or family) — "strong nylon," "clear resin," "high-temp," or a specific grade. Not sure? Describe the use and let them recommend.
Units — mm or inches, plus a reference dimension.
Critical features and tolerances — call out the few features that must be precise (a bearing seat, a mating face). Leave everything else at standard tolerance to keep cost down.
Intended use — prototype, functional end-use part, display model. This tells the provider how much process control you need.
Turnaround — "need it by Friday" versus "no rush" can change both the price and which provider fits.

Copy-paste template: "Attached is a STEP file. I need [qty] of this part in [material/use]. Dimensions are in [mm/inches]; overall length is [X]. The [named feature] is critical to ±[tolerance]; everything else can be standard. It's an [end-use / prototype] part. Hoping for delivery by [date]."

Five Easy Ways to Lower Your Quote

Once your file is clean, these levers reduce cost directly:

Hollow large solid parts where strength allows — less material, lower price.
Batch parts into one order so they nest in a single build and share setup cost.
Don't over-specify tolerances you don't truly need; tight tolerances mean extra finishing.
Reduce unnecessary volume — fillets and lightening pockets cut material.
Pick the right process for the job. For a sense of how process and material drive price, see how much 3D printing costs.

Send It to the Right Providers

A perfectly prepared file still needs the right shop. Send the same file and brief to two or three providers so you can compare price and turnaround fairly.

Browse the 3D Prototyping Hub directory and shortlist providers whose listed processes and materials match your part.
Attach your STEP file and paste the one-paragraph brief.
Compare the quotes on total cost, lead time, and how well each provider understood the part. Our guide to choosing a 3D printing service covers what separates a good response from a bad one.

Ready to get priced? Submit your project through the directory — a clean file and a clear brief is all it takes to get an accurate quote fast.