Problematically, in TNG there is great conflict and contradiction regarding the true speed of the Enterprise. We may suggest it is path-dependent, but estimates clearly conflict as to the speed.
Warp engine efficiency typically floats around 90-95%. Actual fuel milage is aided in practical terms by the use of Bussard collectors. FTL travel is complemented in detail by the complexities of FTL sensors and communications, which appear to be very powerful, but beset by peculiar limitations.
In "Allegiance," Geordi states that operating engine efficiency is 93%. This is improved during the episode to 96%. In a notably similar example in "New Ground," Data notes that the low energy loss of the soliton wave (<2%) makes it 450% more efficient than the warp drive of the Enterprise. This could refer to the efficiency of the warp engines at either a bit over 91%, which would lie closely in line with the above figures, although it could also be interpreted as placing warp drive efficiency at ~21.8%. In "Force of Nature," Geordi brings power conversion to a high of 97.2%.
The existence of the Bussard collectors is noted first in "Samaritan Snare," in which they were used as a dramatic mock-weapon. A Bussard ramscoop is a classic space engine that collects interstellar hydrogen for fuel.
"The Last Outpost" gives the time to go from full reverse impulse to full forward warp as 0.0003 seconds.
"The Battle" tells us that while sensors may be deceived as to the actual location of a warp speed vessel making a Picard Maneuver, they may instantaneously detect and react the displacement of interstellar hydrogen by the deflector and lock a tractor beam on it. In other cases, such as in "Heart of Glory," warp speed vessels are tracked and identified directly via sensors while moving at warp. This can be done consistently at distances of multiple light years, as in "Unnatural Selection," in which a two parsec radius is scanned for vessels in a brief moment.
"Where None Have Gone Before" states that a subspace radio signal would require 51 years and ten months to travel 2.7 million light years.
The various references, from season to season, give no consistent speed.
The Enterprise is flung far out of the galaxy (a billion light years) in "Where None Have Gone Before." While 2.7 million LY off, their estimated return time at maximum warp is ~300 years. A subspace radio signal would take 51 years and 10 months, for a sustained long term warp speed of 9000c and a speed for subspace radio of 52,000c.
In "Conspiracy" 41775.5, the Enterprise turns to Mira, 400 light years from Earth, 41776.1 and then Earth itself 41780.2. Passage of only a few days seems implied, which would give an average speed of 30,000-40,000c. Wherever the Enterprise is in "The Neutral Zone" shortly afterwards, it would take a craft at full impulse power 1200 years to get there, suggesting warp speed to be many thousands of times impulse speed.
"Where Silence Has Lease" 42193.6 heading into the "unexplored" long reach of the Morgana quadrant, the Enterprise happens upon nothingness. After a few moments at warp 2, and then warp four 4 , inertial guidance says 7 parsecs travelled in moments. If this brief moment, which is filled with continuous dialogue and brief puzzled pauses, stretches for a full minute, then warp 2-4 gives an average speed of ~12,000,000c. Later in the episode, the stardate is 42194.7.
"Unnatural Selection" - whenever Geordi pushes past warp 6, he gets a lump in his throat - or so he claims. The Enterprise needs "seconds" to catch up to a vessel moving at maximum warp. Scanning, there are no vessels within 2 whole parsecs. In this episode, we also hear the line "What's a light year among friends?" Gagarin four was visited 3 days prior to the Enterprise by the USS Lantree. They arrive three hours after making comm contact, shortly after examining the ship. This gives (given Gagarin IV being more than two parsecs away) a speed of at least 18,000c for the Enterprise and a cruise speed of over 800c for the USS Lantree.
In "The Dauphin," after cruising at impulse for a while, warp 8.8 will bring the Enterprise to another star system in 3 hours and 9 minutes; this suggests a rushed speed of 10,000c or more ordinarily, but could easily point to an order of magnitude more or less.
The Enterprise returns to the Neutral Zone in "Contagion" 42609.1; They are then well beyond where any late 21st century ship could've traveled on its own in "The Royale" 42625.4, and where no manned Federation ship has travelled before in "Time Squared" 42679.2. Six hours later, the stardate is 42679.5. In "Pen Pals" 42680.3 they are the first manned vessels in the Selcundi Drema quadrant.
"The Icarus Factor" - Sector Omicron-Vega is "months away even at high warp," and the Enterprise returns to Earth around stardate 42686.4. That the Enterprise can move from in unexplored territory to the heart of the Federation in roughly a week, while the furthest reach of the Federation is months away, suggests either contradiction or a very porous shape.
In "Q Who" they are sidetracked and thrown 7,000 light years off course; returning to base would take over two and a half years, setting sustained warp speed over a long haul at 2700c.
The Enterprise goes "far" from Picard to a
distress signal in the distant Rhomboid Droganar Sector, but returns
when Dr. Pulaski is needed to finish surgery on Picard, then proceeds
to the Epsilon Sector. This brings them to the Ficus Quadrant.
In "Up the Long Ladder," they cruise
at warp 5 ... and, after some time, have an ETA of 18 hours for a 0.5
light year trip, giving a speed of perhaps 243.5c for warp 5.
A Class 8 probe is designed to go
warp 9 on a 2 meter long chassis... and could conceivably carry a
person and life support, and transport is possible at that speed, as in "Emissary." The Klingon Empire
had received a message two days earlier.
In "The Enemy," Galorndon Core is a
half light year away from the Neutral Zone. When at the NZ-Romulan
border line, a Romulan vessel is six hours' travel away - and five
hours from the Federation border, giving a speed of 4383c. At this pace, the Romulan vessel
can tell with absolute certainty twenty nine minutes from the border
that the Enterprise is not at the edge of the border (i.e., a quarter
"The Price" places a warp 9 trip
from past the Denkiri Arm in the Gamma Quadrant as "nearly a century," and Picard
estimates that the Ferengi would take nearly eighty years to reach it
(presumably at warp nine). 200 light years away from the intended
terminus, Geordi and Data are ~70,000 light years from where they
began, placing warp nine at somewhat more than 700c and Ferengi sustained safe
cruising speeds at 875c.
The Enterprise finally returns to
known space after "Vengeance
heading to Alpha Leonis. In "The
Defector," we have a 41 second ETA given and a visible position
within the NZ; from the border of the NZ to Starfleet Command on Lya
Three, there is a 2 hour 22 minute transmission delay.
In "Deja Q," the Enterprise extends
its warp field around a small moon in an atmosphere-skimming orbit,
reducing its gravitational constant and somehow therefore its effective
In "Allegiance," the nearest pulsar
is over in the Lonka cluster, 34 minutes away at warp 7 - and 31 hours
at warp 2. This places warp 7 as 54.7 times as fast as warp 2.
Jovis, in "The Most Toys," apparently has a
maximum speed of warp three. 23 hours after the encounter, the
Enterprise has returned from a visit to another system and Wesley offers
the estimate of a 0.102 light year perimeter for searching, placing warp
3 at 38.9c.
In "Transfigurations," the
Enterprise sets course for a pulsar 2.3 parsecs away, with an ETA of
almost 3 weeks, giving a speed of ~130c.
In "Brothers," the trip back from
Soong's abode to Starbase 416 took likely less than 24 hours. How much
less, or how far, is unclear.
In "Suddenly Human," a Talarian ship "halfway through the Woden sector"
will arrive in hours at maximum warp.
"The Wounded" establishes the
Enterprise as being able to detect a fellow UFP starship at a range of
ten light years. A warp 9 intercept course, set immediately after
detection, has an ETA of 22 minutes. This gives a relative speed of
240,000c between the two ships.
A warp 4 intercept while tracking the Pheonix gives a time of 16 hours
and 44 minutes; warp 4 is therefore less than 5240c.
"Clues" gives us Riker referring
to 0.54 parsecs as a "day's
travel," placing cruising speed at 643c. The speed used to return is warp
2; we may hazard to guess that this is the normal speed for traveling
within wormhole infested nebulae.
"Galaxy's Child" - it's possible
for interference to prevent the formation of a warp field.
In "Night Terrors," the Enterprise
is far enough that a response is not expected to a subspace radio call
for 24 days; they were coming in response to a distress call sent 29
"The Nth Degree" - Enterprise
goes 30,000 light years with modifications from a 1400-1500 IQ Barclay,
within a minute's travel or so - roughly 16 billion c.
"In Theory" - Picard orders a
three quarters impulse course to a planet three light years away.
"New Ground" explores a new warp
technology. When the wave is moving warp 6.37, an estimate for impact
(including acceleration) with a planet 3 light years away is "about two hours." This places
warp 6.37 at less than 13150c.
"Descent" - while on patrol of a
sector with 15 starships, ETA to New Berlin is 15.5 minutes at warp
nine. Given the number of systems involved (this is the third such alarm
of the day), it seems likely, but not necessarily, that the Enterprise was 1-5 light years away,
suggesting a speed of 34,000-170,000c.
Transwarp conduits are at least "twenty
times" the top warp speed available to the Enterprise.
"Descent" - Beverly drops out of
warp around a planet with the Enterprise. Hiding in a sun, they consider
going directly to warp upon exiting its corona.
In "Liasons," Picard has an ETA of
17 hours 32 minutes to the Iyaaran homeworld shortly prior to
crash-landing in another system. This suggests shuttle speeds in excess
In "Interface," the Hera had a last reported position "over three hundred light years"
from the gas giant; a day after the Hera
has been missing for four, that position was ten days' time in the past.
This represents 300-400 light years travelled in ~5 days, for a cruising
speed of ~22,000-29,000c.
"Gambit" - a ship can go straight
to a speed of warp 8.7 from planetary orbit. The Enterprise can easily outpace that
ship by a factor of 2.8 at warp 9.
"Force of Nature" - searching a
12 light year corridor will take 2 days, i.e., a minimum average speed
of ~2200c if a single pass is
sufficient to search the corridor. A warp pulse can carry a ship for two
minutes without using the warp drive.