The trade-off in plain terms
A smithy level gives every future (and existing) unit of that type a permanent combat stat bump, but it costs resources up front and doesn't add a single extra unit to your army today. Training instead adds bodies immediately, at full current stats, with no lasting upgrade. If you only ever fielded one unit for one battle, training would always win. The reason upgrades matter is that the stat bump applies to every unit of that type you'll ever field afterward, so the value compounds with army size and time.
That compounding is exactly why there's a real break-even count rather than a universal answer: below a certain army size, spending on training gets you more raw fighting power sooner; above it, the same resources spent on a smithy level eventually out-produce what training would have given you, because the upgrade is multiplying a bigger base.
Why the answer changes by tribe and unit
Unit costs, base stats, and smithy upgrade costs are not the same across Romans, Gauls, Teutons, and the other tribes, so a break-even count that works for one tribe's main infantry can be wildly wrong for another tribe's cavalry. Cheap, fast-training units usually favor training longer before upgrades pay off, since you can replace losses quickly anyway; expensive, slow-training elite units tend to favor upgrading earlier, because losing an unupgraded elite unit is a much bigger sunk cost.
Your time horizon matters just as much as the unit. If you're training a defensive garrison you expect to hold for the rest of the server, upgrades pay for themselves many times over. If you're throwing together a one-off raiding party you'll spend within days, the upgrade may never break even before the army's job is already done.
Running the actual numbers instead of guessing
Because the break-even point depends on current smithy level, target level, unit costs, and how many units you're already committed to training, it's not something to eyeball. Our Smithy Upgrade vs Training Calculator takes your tribe, unit, and current levels and gives you the exact troop count where upgrading starts winning, so you can decide with numbers instead of instinct before you commit a queue.
Common questions
Is it ever better to train troops than upgrade the smithy?
Yes, below a certain army size training more units gets you more raw fighting power sooner, since a smithy upgrade only pays off once it's multiplying a large enough base of existing and future units.
Does the smithy upgrade apply to troops I already have?
Yes, a smithy level's combat stat bump applies to every unit of that type you already own as well as every one you train afterward, which is why the upgrade's value compounds with army size.
Why is the break-even point different for every tribe?
Unit costs, base stats, and smithy upgrade costs all differ between Romans, Gauls, Teutons, and the other tribes, so a break-even troop count that holds for one tribe's unit can be wrong for another tribe's unit entirely.