Travel software & APIs Travel technology glossary

Look-to-book ratioLook-to-book (L2B) ratio

Also called L2Blook to booksearch-to-book ratioshop-to-book ratio

Definition

The look-to-book ratio (L2B) is the number of availability or shopping requests a travel seller sends to a supplier system for every booking it makes. A ratio of 1,000:1 means a thousand searches per booking. Airlines, GDSs and hotel suppliers track it because every search costs them computing capacity and money.

What Look-to-book ratio means

Every time a traveller searches for a fare, one or more requests travel from the seller to a supplier: an airline system, a GDS or a hotel source. Most searches never become bookings. The look-to-book ratio measures that gap, usually per partner and per month.

Ratios have climbed with online travel. Price-comparison behaviour, metasearch engines querying on behalf of millions of users, and bots all add searches without adding bookings. A 2019 IATA report on NDC scalability gave airline websites ratios of around 100–300 to 1, while OTAs and metasearch engines were at best around 1,000 to 1 and more commonly above 10,000 to 1. Airline system providers and analysts have since warned that AI shopping agents could push volumes much higher.

Because search costs money, suppliers manage it through contracts. Distribution agreements can set an allowable L2B ratio, with excess fees charged per search above the threshold, or reduced access for partners that exceed it. The terms vary by supplier and are rarely public.

Sellers manage their ratio mainly through caching: storing recent results and answering repeat searches without a live call, then confirming the price before booking. Smarter request routing, filtering bots and limiting calendar-style searches that fan out into many calls also help. NDC adds pressure, since airlines compute offers dynamically and cannot rely on filed fares in the same way.

How Look-to-book ratio works

The ratio is simple to calculate; managing it is the hard part.

  1. Count shopping requestsThe supplier or seller logs every availability, pricing or offer request sent in a period, usually by partner or credential.
  2. Count bookingsCompleted bookings, or sometimes ticketed segments or passengers, are counted for the same period.
  3. DivideRequests divided by bookings gives the ratio, for example 2,500,000 searches and 1,000 bookings equals 2,500:1.
  4. Compare with the agreed limitIf a contract sets a maximum ratio, the supplier compares actual and allowed levels and may charge or restrict access.
  5. Reduce unproductive searchesThe seller adjusts caching, filters bots and tunes routing so fewer requests reach the supplier for each booking.

Look-to-book ratio in practice

Calculation (illustrative): an OTA sends an airline 30 million NDC shopping requests in a month and makes 6,000 bookings. Its look-to-book ratio is 5,000:1. If its agreement allows 3,000:1, the extra 12 million requests may attract an excess-search fee or a throttle on traffic.

Industry levels: the IATA 2019 NDC scalability report noted that letting metasearch engines query airline offer systems directly from the first search can raise ratios by a factor of about three to five, and expected ratios to stay in the several thousands to one even with mitigation. In 2015, Amadeus said many airline systems were at about 1,000:1, according to PhocusWire.

Caching (illustrative): a B2B portal caches Dubai to London fares for 15 minutes. Agents searching the same dates within that window see cached results, and only the final price check before booking calls the airline.

Who uses it

AirlinesMonitor the ratio by channel and partner to control the cost of answering shopping requests and to set fair access terms.
OTAs and metasearch enginesManage caching and request volumes to stay within contracted ratios and avoid excess-search charges.
GDSs and aggregatorsBalance search traffic from many sellers against the capacity and terms of the airline and hotel systems behind them.
B2B portals and travel agenciesTrack their own ratio when using supplier APIs with usage limits, and tune their booking engine to avoid wasted calls.

Advantages and limitations

Advantages

  • Gives suppliers a clear, comparable measure of how efficiently each partner uses their systems.
  • Helps sellers identify bots, broken integrations or wasteful search patterns.
  • Supports fair cost sharing when partners generate very different search volumes per booking.
  • Encourages caching and smarter request design that improve response times for travellers.

Limitations

  • A single ratio does not distinguish valuable searches from bot traffic or research that leads to a later booking elsewhere.
  • Caching to improve the ratio can show stale prices, causing price changes at booking.
  • Contract thresholds and fees differ widely and are rarely published, so comparisons between partners are hard.
  • Dynamic and personalised offers in NDC are harder to cache, so ratios may rise as airlines move to offer-based selling.

Frequently asked questions about Look-to-book ratio

What is a good look-to-book ratio?

There is no universal benchmark; it depends on channel and market. IATA's 2019 report put airline websites at roughly 100–300 searches per booking and found OTAs and metasearch engines commonly far higher. A good ratio is one within the limits agreed with each supplier and stable over time.

Why do airlines charge for excess searches?

Each search uses airline or GDS computing resources, and with dynamic offers the airline may calculate a new price every time. When a partner sends far more searches per booking than agreed, the airline bears cost without matching revenue. Excess-search fees or throttling recover some of that cost.

How can a travel agency reduce its look-to-book ratio?

Cache popular routes and dates for short periods, block bot traffic, avoid launching wide calendar or multi-airport searches by default, and only call live pricing when a traveller shows intent, such as selecting a flight. Monitoring searches per booking by source helps find integrations that are wasting calls.

Will AI travel agents affect look-to-book ratios?

Industry voices expect so. AI agents can run many searches to answer one question, and airline technology firms have warned that this could multiply search volumes per booking. Proposed responses include stronger caching, indicative pricing before live calls, and new layers that guide agents before they query airline systems.

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Sources and further reading

  1. IATA — Addressing NDC scalability challenges in the leisure market (2019)
  2. PhocusWire — Airline system look-to-book ratios soar, expected to go 10x higher
  3. PhocusWire — Look-to-book: AI and the rising cost of search for airlines
  4. AltexSoft — Look-to-book ratio in aviation
  5. Law Insider — Look-to-book ratio clause samples