Calculate watts based on age, height, weight, trainer, etc?

After a few months, I decided to participate in a race at the slowest level possible. Apparently I’m still the slowest rider in Zwift history.

My question: What formula does zwift use to calculate my watts? I want to make sure that the number of watts I’m seeing in the screen is correct. Does is use anything else besides age, height, weight, bike, trainer, current gear, and RPMs? I have a Kinetic Fluid Trainer Road Machine with InRide Sensor.

I don’t want an exact number, but I would like to confirm that the watts displayed in zwift is precise.


It depends on what trainer or powermeter you use. If you use a powermeter or smart trainer then zwift use the power number that the trainer or powermeter send to zwift.
If you use a wheel on classic trainer with a speed sensor then zwift use the wheel speed and a power-speed curve for the trainer to calculate the power number.

I have a Kinetic Fluid Trainer Road Machine with InRide Sensor

Does anyone know how to calculate the watts?

no you are not the slowest I am.

Watts for a non-smart trainer are calculated the following way. It takes your rear wheel speed and the power curve of the trainer you selected. Also make sure you are choosing the correct wheel size.

If it is a smart trainer (one that broadcast watts) then there is no calculations done, it’s just the watts that are being broadcast from the trainer.

With those watts, weight entered, height entered, in-game bike used, in-game wheel set used, in-game drafting and virtual elevation changes your in-game speed is determined.

So this is how a Classic trainer like your Kinetic work.

Zwift have a Power (watt) vs Speed (km/h)

So your speed sensor send zwift your wheel speed, in this case 37km/h then Zwift read of the curve and find 340w.

Every classic trainer has it’s own power-speed curve.

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But only certain ones are supported by Zwift, so make sure you select the correct one on the pairing screen!

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So let’s say these are the values:

Height: 180cm
Weight: 175 lbs
Age: 40
Trainer: Kinetic Fluid Trainer Road Machine with InRide Sensor
RPM: 72
Flat route

What should the watts be?

Zwift have their own internal formulas. You also need more information like what gear and wheel speed.

Age, weight and weight has no part in calculating power. Power = torque x speed.

150 watts approximately,

Lol no. Get a powermeter or smart trainer

I have 3/4 a tank of gas and I had pasta for dinner, can you tell me what my waist size is?

I have the same trainer and also use the InRide sensor.

As you have found out, and the others may not know, there is no wheel selecting for this setup.
The sensor just reports how fast the resistance unit is turning and reports the watts.

This was tested by DC Raonmaker and was found to be very accurate.

But, you should calibrate it using the Kenetic app after warming up the resistance unit (20 min).

I really don’t understand all the technical stuff but, I had calibrated and used this trainer in the summer with an older MTN bike.
When Winter came and I put my road bike on, I was very dissatisfied with my power output.
I then remembered I had not calibrated using my current bike and that seemed to help.

Of course, it is nothing like the old Z Power days.