Why Your $4/Hour Formula Leaves Money on the Table

Where the Formula Comes From

The $4/hour method has been floating around Reddit, YouTube, and 3D printing forums for years. The logic seems sound: your printer costs money to run, filament costs money to buy, so charge for both and double the material to build in some profit.

For casual printing — making a friend a phone stand, or splitting costs on a D&D mini — it's fine. But if you're trying to run an actual business selling prints on eBay, Etsy, or your own site, this formula has blind spots that compound into real money left behind.

What $4/Hour Actually Covers

Let's break down what $4 per hour of print time is supposed to pay for. If you're running a Bambu X1C that cost $1,200 with an expected lifespan of around 6,000 hours, your depreciation cost is $0.20 per hour. Electricity for a 350W printer at $0.13/kWh adds roughly $0.05 per hour. That's $0.25 in real machine costs.

So the $4/hour rate gives you $3.75 per hour above your actual machine costs. That sounds like margin — until you account for everything the formula ignores.

The Five Hidden Costs

1. Your Labor Time

The $4/hour formula doesn't include a single minute of your time. But every print requires setup: loading filament, slicing, starting the job, checking first layers. Then post-processing: removing supports, sanding, cleaning the build plate. Then packaging and shipping. A "4-hour print" easily takes 30-45 minutes of your hands-on time.

If you value your time at even $20/hour, that's $10-15 per order that the formula completely ignores.

2. Failed Prints

Not every print succeeds. Bed adhesion fails, filament tangles, power flickers, and sometimes the model just doesn't work. If you're running ASA, your failure rate might be 5-10%. Running TPU or nylon? Higher. Every failed print costs you material, machine time, and electricity with zero revenue.

A realistic failure buffer of 5-10% on top of your costs protects your margins from the inevitable bad print.

3. Marketplace Fees

eBay takes approximately 13.25% of your final sale price. Etsy takes 6.5% plus $0.20 per listing. Amazon takes 15%. If you're pricing at $20 using the simple formula and selling on eBay, $2.65 immediately disappears to fees — and that's before PayPal or payment processing takes another cut.

4. Packaging and Shipping Supplies

Bubble mailers, poly bags, labels, tape, padding — it adds up. A typical small shipment costs $1-2 in packaging materials alone, on top of the actual postage. The $4/hour formula treats packaging as though it's free.

5. Machine Depreciation (Real Numbers)

The $4/hour rate roughly covers depreciation — but only if you actually run your printer 5,000+ hours over its life. Most hobby-to-business sellers run their machines 2-4 hours per day. At that rate, the depreciation cost per hour goes up significantly because you're spreading the purchase price over fewer total hours.

A Real Example

Let's price a typical product: a set of RV cabinet door catches printed in ASA. 75 grams of filament, 4 hours of print time, 15 minutes of setup, 10 minutes of post-processing, sold on eBay.

The $4/Hour Method

$4 × 4 hours = $16, plus material doubled: ($28/kg × 0.075kg) × 2 = $4.20. Total: $20.20

The Real Cost Method

Material: $2.10. Machine depreciation: $0.80. Electricity: $0.18. Labor (25 min at $25/hr): $10.42. Failure buffer (8%): $1.08. Packaging: $1.25. eBay fee (13.25%): roughly $4.50 on a $34 listing. Shipping supplies and handling: $5.50.

True cost: approximately $25.83. To hit a 40% margin, you'd need to list around $34.

The $4/hour formula had you at $20.20 — almost $14 below what you should be charging. On that $20 listing, your actual profit after all costs is barely $2. That's not a margin — that's a rounding error.

When Simple Formulas Do Work

The $4/hour formula isn't useless — it's just incomplete. It works reasonably well for quick quotes on low-value commodity prints where your labor is minimal, failure rates are near zero, and you're selling direct (no marketplace fees). Benchy-style trinkets at a craft fair, for example.

But for anything involving premium materials, post-processing, marketplace selling, or parts where customers are paying for a specific solution (replacement parts, functional hardware), you need the full cost picture.

See the difference for yourself

Plug your actual numbers into the FilamentMath calculator and compare what the common formulas suggest vs. what you should actually charge.

Open Calculator →

Discussion

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