One mile running equals three miles cycling. You've heard it. It's not wrong, exactly — but it's about as precise as saying a pint of Guinness equals a glass of wine. Here's the real maths.
The question matters more than it looks. Runners moving load onto the bike, cyclists adding run days, triathletes juggling both, anyone coming back from injury and wondering what a 40K ride is "worth" against the 10K they were supposed to run — they all need some exchange rate between the sports. Get it roughly right and your training week holds together. Get it badly wrong and you either train half as much as you think or dig a fatigue hole while your log says you're taking it easy.
So let's do this properly: where the 1:3 rule comes from, where it collapses, and the conversions that actually hold up.
Where the 1:3 rule comes from
The ratio isn't arbitrary. At everyday recreational intensities, the energy arithmetic lands close to it.
A 70kg runner covering a mile at a moderate 9-10 minutes burns roughly 100 calories. The same rider cruising at 15-16 mph on flat roads burns roughly 30-40 calories per mile. Three-ish cycling miles per running mile. The effort comparison tells a similar story: that runner's mile takes about nine minutes at a moderately hard effort; three miles of moderate riding takes eleven or twelve. Close enough that the rule survived decades of club-run folklore.
And for casual planning at casual speeds, it works. A gentle 5K run and a gentle 15K spin are comparable sessions. Nobody needs a sports scientist for that.
The trouble starts the moment anything gets fast, hilly, or windy.
Why the ratio breaks: the physics
Running and cycling have fundamentally different cost structures, and the 1:3 rule quietly assumes both away.
Running cost is nearly flat. The energy cost of running is set almost entirely by body weight times distance — roughly 100 calories per mile for a 70kg runner whether they run it in 7 minutes or 11. Faster running burns more per minute but covers the mile sooner; the two nearly cancel. This is one of the tidiest findings in exercise physiology, and it's why runners can plan by mileage alone and get away with it.
Cycling cost is anything but flat. On a bike, your body weight is supported and rolling resistance is small; at speed, the dominant force you're fighting is air. And aerodynamic drag rises with the square of speed — which means the power to overcome it rises with the cube. Ride twice as fast and you need roughly eight times the power against the wind.
Sit with that for a second, because it demolishes any fixed distance ratio. A mile at 30mph costs several times the energy of a mile at 15mph. Same mile, wildly different price. A 20-mile ride could be a recovery spin or a leg-shredding chaingang effort, and the odometer can't tell the difference. Meanwhile a 6-mile run is a 6-mile run, give or take.
So the defensible statement is: one running mile equals three cycling miles at moderate speeds on flat roads with no wind and no drafting. Add a group to sit in, a climb, or a tailwind, and the ratio wanders anywhere from 1:2 to 1:5.
Hills deserve their own sentence, because they break the ratio in both directions at once. Climbing at 8kph up a 10% gradient is some of the hardest work in endurance sport — and it produces almost no distance. A hilly 40K ride can out-cost a flat 70K one. Descending is the mirror image: kilometres for free, heart rate at rest. Any distance-based conversion treats those kilometres identically, which tells you everything about how much to trust it.
Time is a better currency than distance
Once you stop counting miles and start counting minutes at a given effort, the comparison gets much sturdier.
The working rule: 30 minutes of running at moderate effort ≈ 45-60 minutes of cycling at moderate effort for comparable training stress.
Why isn't it 1:1? Because running is the less efficient — and therefore more potent — exercise per minute. Every stride lifts and lowers your entire body weight against gravity, loads muscle eccentrically, and recruits your trunk and upper body for stabilisation. Cycling supports your weight on the saddle, involves no impact, and lets you coast. Heart rates run several beats lower on the bike at equivalent perceived effort, and the muscular systems are under far less total strain per minute.
This is precisely why running is the time-crunched athlete's weapon — maximum stimulus per minute — and why cycling is the volume athlete's weapon: because it's gentler per minute, you can pile up hours that would destroy you as running mileage. A 20-hour cycling week is routine for amateurs; a 20-hour running week is elite-marathoner territory that most bodies simply cannot absorb. Same currency, different denominations — and the weekly scheduling guide shows how to spend both in one week without going broke.
The calorie view
For anyone converting sessions with an eye on fuelling or weight management, the calorie framing is worth spelling out separately.
Running: roughly your body weight in kilograms, in calories, per kilometre — which shakes out near 100 calories per mile for a 70kg athlete, largely pace-independent. Cycling: entirely context-dependent. That same 70kg rider might burn 400 calories in an easy hour or 900+ in a hard one, depending on speed, terrain, wind, and whether there's a wheel to hide behind.
Consequence: never fuel a ride off a distance-based rule of thumb. A four-hour ride's carbohydrate demand depends on the work done, not the kilometres covered — a power meter's kilojoule reading is the number that doesn't lie, and the fuelling calculator will translate a planned session into an eating plan properly.
The converter that doesn't lie: training stress
If you want one number that compares a run and a ride without lying to you, it exists: TSS — Training Stress Score — or its heart-rate cousin TRIMP.
TSS scores a session from two inputs: how long it lasted and how intense it was relative to your personal threshold. An hour exactly at threshold scores 100, in either sport. An easy hour scores maybe 50-60. A brutal 90 minutes might score 130. Because the score is anchored to your own threshold in each sport — FTP on the bike, threshold pace on foot — it automatically absorbs all the physics that wreck distance ratios. The wind, the drafting, the gradient: all of it is already priced into your power output before TSS ever sees the session.
Same TSS, roughly same training load, regardless of modality. That's the whole trick. A 60 TSS ride can stand in for a 60 TSS run in your weekly load without the accounting going sideways. It's how triathlon coaches have balanced three sports in one athlete's week for two decades, and it's the answer serious multi-sport athletes eventually arrive at.
Two caveats, both important. You need a threshold benchmark in each sport for the scores to mean anything — a stale FTP or guessed threshold pace produces garbage numbers. And TSS equivalence covers aerobic and metabolic load only. Which brings us to the fine print.
The conversion table
With all caveats standing, here are the working equivalences — moderate, steady efforts, matched for overall training stress:
| Run | Ride equivalent | |---|---| | 5K run (~30 min) | 15-20K ride (45-60 min) | | 10K run (~50 min) | 30-40K ride (75-90 min) | | Half marathon (~1:45) | 80-100K ride (~3:00) | | Marathon (~3:30) | 150-180K ride (5:00-6:00) |
Read the pattern: the run-to-ride time ratio stretches as the distances grow, from roughly 1:1.5 at the short end toward 1:1.7 at the long end. Long rides sit at gentler relative intensities than long runs — nobody rides 160K at their half-marathon effort — so they need proportionally more saddle time to bank the same stress.
These are rough equivalences for effort, not exact science. Use them for planning — deciding what Saturday's ride is worth against the run you skipped, roughing out a week that mixes both sports. Don't use them for precision, and don't let anyone on a forum convince you the decimal places exist.
A worked example: converting a real week
Say you're a runner on 50km a week — a 10K of intervals, a couple of easy 8Ks, a midweek 10K tempo, and a Sunday 16K — and a grumpy Achilles means two of those sessions need to move onto the bike for a few weeks.
The two easy 8Ks are the obvious candidates: about 45 minutes each on foot, so roughly 65-75 minutes of genuinely easy Zone 2 riding apiece. Your week now reads: intervals on foot, two easy rides, tempo on foot, long run on foot. Total training time went up by about 40 minutes; total training stress stayed level; impact volume dropped by a third. That's the conversion working exactly as intended — the tendon gets its rest without your fitness paying for it.
What you wouldn't do is convert the tempo run, because that session's value is running-specific, or bolt the saved kilometres onto the remaining runs to "keep the mileage up." The weekly kilometre total is the wrong number to defend. The stress total is the right one.
The same logic runs in reverse for cyclists adding run days — with one big asterisk. A cyclist converting an easy 90-minute ride "owes" only about an hour of easy running by the maths, but tissue that has never absorbed impact can't cash that cheque in one go. Start with 20-30 minutes, whatever the conversion table says your engine can handle, and build from there. The conversions govern aerobic load; your tendons operate on their own schedule.
When to use which conversion
Three tools, three jobs. Use distance ratios for nothing more serious than a sanity check — is this ride roughly in the same postcode as that run? Use time-at-effort for weekly planning: it's accurate enough for substitutions and easy to do in your head. Use TSS or TRIMP when the stakes rise — a triathlon build, a return from injury where load must climb gradually, or any block where both sports carry serious volume and an accounting error means overtraining. And if you're mixing the sports every single week rather than occasionally converting between them, the structural questions — which days, what order, how much impact — matter more than any exchange rate.
What no conversion captures
One asymmetry sits outside every formula on this page, and skipping it would make the whole table dishonest.
Impact doesn't convert. A marathon involves roughly 45,000 footstrikes, each one braking 2-3 times your body weight through muscle that's lengthening under load. That eccentric damage is why marathon recovery takes weeks while a century ride — its aerobic "equivalent" — leaves you stiff for a day. It's also why the conversion only runs cleanly in one direction. A run can substitute for a ride almost perfectly, aerobically and then some. A ride can substitute for a run's engine work but not its tissue work: no quantity of cycling kilometres prepares tendons and bone for pounding, which is exactly why the bike can't replace your long run in the closing weeks of a marathon build — and why cyclists get genuine skeletal benefits from adding even small amounts of running.
Specificity doesn't convert either. Matched TSS means matched load, not matched adaptation. Sixty TSS of running makes you a better runner in ways sixty TSS of riding never will, and vice versa. The conversions keep your fatigue accounting honest; they don't make the sports interchangeable. What actually crosses over between them — and what stubbornly doesn't — is a topic of its own, covered in the cross-training guide.
The takeaway
Keep the 1:3 rule for café conversation. For planning, convert time at effort: half an hour of running buys 45-60 minutes of riding. For precision, let TSS do the accounting, anchored to a current threshold in each sport. And for anything structural — race preparation, bone health, tissue tolerance — stop converting altogether, because impact has no exchange rate.
A pint of Guinness and a glass of wine will both do the job. Just know which one you're pouring, and why.