Treadmill Pace Calculator

What does this calculator do?

The treadmill pace converter matches oxygen cost, not belt speed. In one direction it takes a treadmill speed and grade and returns the flat outdoor pace with the same ACSM running VO₂. In the other it takes an outdoor speed (still entered in km/h) and a grade, and returns the slower belt speed that costs the same.

Typical uses: turning 10 km/h @ 1% into a road pace, finding a belt speed that matches your outdoor easy run, and seeing how 0%, 1%, 2%, 3% and 5% sit next to each other. It does not calibrate a mis-set belt, and it does not add wind, heat or a 1% “air resistance” fudge on top of ACSM.

How does it work?

Speed in km/h becomes metres per minute. ACSM’s running equation gives VO₂ = 0.2v + 0.9v×grade + 3.5. To go treadmill → outdoor we invert the flat equation (grade 0) for a velocity with that same VO₂. To go outdoor → treadmill we invert with the chosen grade in the denominator. The 3.5 rest term cancels, so only the running cost is matched.

Jones & Doust (1996) found that a 1% grade at the same displayed speed best matched outdoor energy cost in still air. This page does not do that. At 10 km/h and 1%, ACSM says the outdoor equivalent is faster than 6:00/km, because you are already climbing. Use 1% as a common indoor setting if you like; do not expect the converted pace to stay 6:00.

Formula

v (m/min) = speed(km/h) × 1000 / 60
VO2      = 0.2 v + 0.9 v × (grade%/100) + 3.5     // ACSM running

treadmill → outdoor (flat)
  v_flat = (VO2 − 3.5) / 0.2
  pace   = 1000 / v_flat × 60                // s/km

outdoor → treadmill at grade g
  v_belt = (VO2_flat − 3.5) / (0.2 + 0.9 × g/100)
  km/h   = v_belt × 60 / 1000

Paces are rounded to a second, belt speed to one decimal. At 0% both directions are identities. The km/h box is the speed you convert from: belt speed in the first direction, outdoor speed in the second.

Worked example

How to interpret the result

A faster outdoor equivalent means the treadmill session at that grade was metabolically harder than the same km/h on the flat. It is not a promise that you would actually run 5:44 outside — no wind, no camber, a calibrated belt.

If you follow Jones & Doust and simply set 1% to “feel like the road” at the same speed, you do not need this converter for that trick. Use it when the grade is the workout (hills) or when you want ACSM-equal sessions. Calories at the same speed and grade are on the running calorie calculator. Unit-only conversions (km/h ↔ min/km) are on the pace converter.

Assumptions and limitations

Assumptions

• The ACSM running equation applies (running, not walking).
• Outdoor comparison is dead-flat, still air, no belt calibration error.
• The km/h value is already in the direction you selected (belt vs outdoor).

Limitations

• ACSM equal-VO₂ is not Jones & Doust’s 1% same-speed rule. At 1% this page will change the pace; their protocol keeps it.
• Treadmill displays are often a few percent fast or slow. This page cannot see a calibration error.
• No air resistance, fan, heat or downhill model. Negative grades are rejected (0–15% only).
• Walking speeds are out of range. Speeds below 8 km/h or above 22 km/h are rejected.
• Fan-cooled “outdoor” on a treadmill is still not a road. Treat the number as metabolic matching, not race pace.
• The comparison table always uses the entered km/h as the starting speed, in both columns.

Methodology and sources

Method type: Published model

Conversions implement the ACSM running metabolic equation, inverted for flat outdoor pace or for belt speed at a chosen grade. Jones & Doust (1996) is cited for the common 1% indoor convention; it is not the formula this page solves. Results are metabolic equivalents, not a calibrated belt.

• Methodology: Treadmill and outdoor pace
• Methodology: Rounding and displayed precision

Sources: ACSM metabolic equations · Jones & Doust 1996

Last reviewed: October 5, 2026