Block Size is a current Regulation NMS defined term. This guide preserves both alternative thresholds in the rule rather than reducing the definition to a single share-count test.
ReviewedEvidence1 sourceSectionPhrases & Idioms
Quick answer
Under Regulation NMS, an order is block size if it is at least 10,000 shares or has a stock market value of at least $200,000.
Key details
Canonical FormBlock Size
Core MeaningAn order is block size if it is at least 10,000 shares or is for stock with a market value of at least $200,000.
Further guidance
History Boundary
This page reflects the current reviewed 17 CFR § 242.600 definition and should be rechecked if Regulation NMS changes.
Meaning
17 CFR § 242.600 defines block size with respect to an order by either a 10,000-share threshold or a $200,000 market-value threshold.
Usage Boundary
This is the Regulation NMS order-size definition; it should not be generalized to unrelated uses of “block” in finance or computing.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
Under current U.S. Regulation NMS definitions, aggregate quotation size is the sum of the quotation sizes of all responsible brokers or dealers communicating bids or offers in an NMS security at the same price. Treat this as a U.S. securities-regulation definition; it should not be generalized to unrelated uses of aggregate size or quotation outside Regulation NMS.
Categorized by Order Size is a current Regulation NMS defined term. This guide keeps the reporting classification tied to the enumerated rule buckets rather than informal size labels.
Under current U.S. Regulation NMS, the “order size benchmark” measures the full displayed size of protected quotations at the national best bid or offer for the relevant side of an order, with special timing for midpoint-or-better limit orders and a cap at the order size. Use the detailed § 242.600 definition for reporting analysis; the benchmark depends on order side and timing and should not be flattened into a generic order-size metric.
Under current U.S. Regulation NMS definitions, published aggregate quotation size is the aggregate quotation size calculated by a national securities exchange and displayed by a vendor when the order is presented to the responsible broker or dealer. This is a Regulation NMS term tied to the regulatory display context; do not collapse it into ordinary aggregate quotation size or general market-depth terminology.
Under current U.S. Regulation NMS definitions, published quotation size is a responsible broker-dealer quotation size communicated under the applicable rule and displayed by a vendor when the order is presented. This is a U.S. Regulation NMS definition and should be kept distinct from aggregate quotation size and broader non-regulatory uses of displayed size.
Under current U.S. Regulation NMS definitions, quotation size is the aggregate number of shares of an NMS security a national securities exchange or national securities association displays at a quoted price. Keep the definition tied to Regulation NMS and the rule-defined displayed-share context; do not generalize it to every platform’s informal use of size.
Tick size is the minimum pricing increment permitted for quotations or orders under the applicable market rule. Tick size is a permitted price increment, not the observed bid-ask spread; a spread can span one or many ticks and the applicable rule can vary by market and instrument.
