Lot Size Limit
A cap on the maximum position size a trader can open at once, or across all open positions combined.
Definition
A lot size limit is a cap on how much capital the trader can allocate to a single position (per-trade limit) or to all open positions combined (aggregate limit). Limits are usually expressed in standard lots for forex (1 lot = 100,000 units) or in contracts for futures. The limit typically scales with account size: a $25K account might be capped at 1 lot, a $100K at 4 lots, a $200K at 8 lots. Exceeding the limit can either invalidate the trade, auto-close the excess, or breach the account depending on the firm.
Example
Why It Matters
Lot size limits are most punishing for traders who size positions aggressively during evaluations, expecting the discipline to carry over. A 2% risk on a $100K account might require a 4-lot position on a 50-pip stop — fine under most per-trade limits, but an aggregate cap across multiple open pairs can bind unexpectedly. Traders with strategies that layer into positions (two half-size entries) need to verify that aggregate exposure stays within the cap across the full layered position.