Three ways to say the same speed
A treadmill shows mph or km/h; a training plan says minutes per mile or per kilometre. All four describe the same belt. The calculator converts in both directions and adds the race times that the speed would produce, which is the quickest way to sanity-check a workout before you start it.
Incline changes the effort, not the display
The belt still moves at the same speed when you raise the incline, but the oxygen cost rises steeply — roughly 3–4% per 1% of grade. The table in the result shows what each incline is equivalent to on the flat, so a 6.5 mph run at 3% is really a 7.4 mph effort.
Why 1% is the default correction
Indoor running has no air resistance, which makes it slightly easier than running outdoors at the same pace. A 1% incline replaces most of that difference for typical speeds. It is an approximation, not a rule, and it matters less at slow speeds.
Frequently Asked Questions
Is treadmill distance accurate?
Belt speed is accurate; stride length is not. Holding the rails reduces the effective load, and overstriding can inflate the distance you think you covered.
How fast is 12 km/h in mph?
12 km/h is 7.46 mph, or 5:00 per kilometre and 8:03 per mile.
Does incline affect the pace shown?
No. The display keeps showing belt speed. The calculator's flat-equivalent column is what your body is actually doing.
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Privacy & your data
SwimRunPace calculates everything in your browser. Distances, times and body weights are never uploaded — there is no account, no server-side record and no training history stored between visits.