Swim Economy calculator (VO₂ to swim time)

What it does

The Swim Economy calculator projects swim time at a given distance based on VO2max, an economy tier (how efficient your stroke is), and environmental modifiers. Use it to set realistic target swim times when you have VO2max from a lab test but want to project to a race distance.

URL: /calculators/ then open the Swim economy entry. Direct path: /static/calculators/swim_economy_calculator.html.

Inputs the form asks for

Distance

Distance: pick a preset (200, 400, 800, 1500, 1900, 3800 m) or enter a custom distance in metres.

Physiology

VO2max (ml/kg/min).
Body mass (kg).
Economy tier: a qualitative choice of how efficient you are (elite, advanced, intermediate, beginner). Drives the cost-of-transport modifier.
Cr (cost of transport): optional override if you know your Cr from a swim economy test directly. If left blank, the tier picks a default Cr.
Fraction of VO2max: what percentage of VO2max you can hold for the target distance (typical race values: 85 to 95% for short, 70 to 85% for long).

Environment

Environment: pool, lake, ocean.
Drafting: yes / no (drafting reduces effective Cr).
Chop / conditions: calm, light chop, rough.

Outputs

Projected swim time at the target distance.
The implied average pace per 100 m.

How it differs from the CSS calculator

CSS is a measured threshold from a test in the water; it tells you what you can hold.
Swim Economy is a top-down projection from VO2max and economy assumptions; it tells you what you could hold if your economy matched the tier.

A gap between the two reveals technique vs fitness limiters.

When to use it

You have a recent lab VO2max but no recent CSS test.
You want a sanity check on what target swim time is plausible.
You want to model the value of improving swim economy by one tier (typical: 30 to 90 seconds gain per 1500 m).