I don't actually know my factory's capacity.

Adding up available hours across the floor produces a comforting number and a useless one. Your factory can only ship as fast as the bottleneck can finish. Every other station has spare capacity by definition. Counting that spare as 'available' is how overpromising starts.

The bottleneck is not a defect in the plant. It is the plant's true capacity, sitting in one place. Once you treat it that way, quotes and due dates stop being theatre. They become a function of how much of that station's time is already spoken for.

We find the bottleneck and measure what it actually finishes in a week — not what it theoretically could if nothing went wrong. That number is your throughput. Everything else is commentary.

From there, sales and planning share one picture: how much bottleneck time each job needs, and how much is left. You can still say yes. You just stop saying yes in the dark.