Time + Power or Time + HR depending on my workout. I ignore miles, speed, etc.

Always record 1 hour on the trainer as 20 miles.

My badger bike miles.

That makes a lot more sense.....I guess that's the problem with going with an off-the-shelf 70.3 training plan that specifies miles instead of time.

oh gawd, a plan with miles....

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Eric Reid AeroFit | Instagram Portfolio
Aerodynamic Retul Bike Fitting

“You are experiencing the criminal coverup of a foreign backed fascist hostile takeover of a mafia shakedown of an authoritarian religious slow motion coup. Persuade people to vote for Democracy.”

+1 on this one. Miles don't take into account terrain, wind or how hard you actually ride. You would be better off relying on time + perceived effort as a minimum.

Yep, indoors is just hours and powers.

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Shane Miller - GPLama
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Your body knows time & intensity not miles.

X2 to what Eric said

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Brian Stover USAT LII
Accelerate3 Coaching
Insta

As others have said, miles on the bike are not an important metric to track, indoors or outdoors. I do look at my miles once a year or so, in the context of, "oh look, I rode x number of miles this year" and for that zwift miles count, haha.

In any event, you should be riding kilometers in zwift! You get more xp when you are using the metric setting. 20 xp for 1 KM and 30 xp for 1 mile :)

I've been getting robbed!!!!!

Regardless of Zwift, live metric. IT IS BETTER
YDMNV

Normally indoor miles are more efficient than indoor miles, because you don't have traffic, red lights, downhills etc that make you stop moving your legs. So as a rule of thumb you can say that indoor training is 30% more efficient, because you can stay 100% of the time in your desired power zone(s), which for most of us who live in cities is not achievable. Maybe in the Australian outback you can have similar control as a trainer, but most of us don't.

Normally I would implement this in a way that if I have a 5 hours / 130km ride outdoors on my schedule (26km/h is normally workable for my rides with traffic/terrain), but its raining and I don't want to go out, I select a flat course on ZWIFT with a TT bike and then do the 130km there, with normally around 32 or 33km/h, which then works out to be a 4h ride roughly. This should be a roughly comparable training load for your body. As the races come closer I would opt for the indoor option more frequently, as I normally do roadbike outdoors and TT bike on the trainer, and this gets me used to long hours in TT position.

But yes, this is a workaround based on experiences and feelings. And in metric.

I count Zwift miles as miles. How do you compare it to outdoors? Are you riding on a trail, in Florida, the mountains? Each 4 hour ride in those different locations will give you different distances. Would you discount the Florida miles over the miles climbing a mountain? With that said, I ride Zwift for time not distance.

It's utterly pointless to put a percentage on it. Even as a rule of thumb.
There's a hell of a lot of variation even between urban environments and circumstances. But it's also quite realistic to say a carefully selected route on the outskirts of a city can often provide long continuous uninterrupted efforts.

To give you the extreme version of what you are asking - almost all my miles from Nov until mid March are on my Fatbike on single track. My avg. speed is approximately 10-12km/h, therefore it's only time and effort that matter.

The question I semi-seriously would like to know, is how to convert fatbike single track climbing on snow to road bike pavement climbing?!? It's has to be at least double!

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I think the best would be if you had a power meter with data for each to make the conversion (KJ/mile to KJ/hour). My fat bike doesn't have a power meter, but using heart rate can pretty well approximate; e.g. 1 hour of fat-bike hill climbing @ 150 bpm might be 5 miles, vs. 1 hour of flat road-riding @ 150 bpm 17 miles, vs 1 hr road riding uphill ~8 miles. I pretty much just convert 1hr at zone 2 = 16 miles.