Key Takeaways
- A half marathon is 13.1 miles (21.0975 km); if you’re asking “how many miles is a half marathon,” the exact standard is 13.1094 miles.
- Key checkpoints: halfway at 6.55 miles, about 52.5 laps on a 400 m track, or roughly 4.22 × 5K segments for pacing.
- Use miles (13.1) for training plans and 21.1 km for race-day math; convert with 1 mi = 1.60934 km and 1 km = 0.621371 mi.
- Official courses are precisely measured and certified (with a 0.1% short course prevention factor), so GPS variances don’t change the true 13.1-mile distance.
- Train to the distance: build long runs and insert half marathon–pace blocks, then taper 10–14 days out while keeping intensity.
I remember the first time I asked how many miles a half marathon is. I wanted a clear target not a mystery. A half marathon is 13.1 miles. That number can look big but it becomes doable with a plan.
In this guide I’ll break down what 13.1 miles really means. I’ll share how I visualize the distance and how I set milestones. Whether you’re training for your first race or just curious I’ve got you. Let’s keep it simple and friendly.
How Many Miles Is A Half Marathon?
A half marathon equals 13.1 miles.
I also track the metric distance because race signage uses it. The certified standard equals 21.0975 kilometers.
I map training checkpoints to round numbers. The halfway mark lands at 6.55 miles.
I keep these equivalents handy for pacing and visualization.
| Measure | Value | Context |
|---|---|---|
| Miles | 13.1 | Official half marathon distance |
| Kilometers | 21.0975 | World Athletics road standard |
| Meters | 21097.5 | Course certification value |
| 400 m track laps | 52.5 | Outdoor track estimate |
| 200 m track laps | 105 | Indoor track estimate |
| 5K segments | 4.22 | 4 full 5Ks plus 0.22 |
| 10K plus | 1 × 10K, 1 × 5K, 1 × 1.0975K | Common race signage split |
| Halfway point | 6.55 mi | Even split marker |
Use 13.1 miles for planning, if your training log tracks in miles.
Use 21.1 kilometers for race math, if the course markers post in kilometers.
Use 6.55 miles as a mental anchor, if you pace even halves.
Use 52.5 laps on a 400 m track for simulation, if you practice steady splits.
Use 4.22 × 5K for chunking, if you pace by 5K clocks.
Use landmarks like bridges, park loops, city blocks for visualization, if you train on familiar routes.
I confirm the distance standard from World Athletics and USATF. Sources: World Athletics Road Running distances https://worldathletics.org/records/by-category/road-running, World Athletics Measurement and Certification Procedures https://worldathletics.org/about-iaaf/documents/technical, USATF Course Certification https://www.usatf.org/certification.
Miles And Kilometers: Understanding The Conversion
I anchor half marathon miles to kilometers to keep pacing exact. I use exact constants, then I round for everyday planning.
13.1 Miles Equals 21.1 Kilometers
I convert half marathon miles to kilometers with fixed factors. I use 1 mile equals 1.609344 kilometers and 1 kilometer equals 0.621371 miles.
| Metric | Exact value | Rounded value | Source |
|---|---|---|---|
| Half marathon distance in kilometers | 21.0975 km | 21.1 km | World Athletics Road Race rules, WorldAthletics.org |
| Half marathon distance in miles | 13.1094 mi | 13.1 mi | World Athletics Road Race rules, WorldAthletics.org |
| 1 mile in kilometers | 1.609344 km | 1.61 km | NIST SP 811, nist.gov |
| 1 kilometer in miles | 0.621371 mi | 0.62 mi | NIST SP 811, nist.gov |
I pace long runs with kilometer markers and mile splits as a cross check. I plan visualization with 5K blocks at 3.1 miles each and track laps at 400 meters each.
- Pace anchors: I map 5K at 3.1 miles and 10K at 6.2 miles for segment goals.
- Split math: I multiply mile pace by 1.609 to get kilometer pace and I divide kilometer pace by 0.621 to get mile pace.
- Race signage: I read both mile boards and kilometer boards if the course posts dual markers.
How Courses Are Officially Measured
I rely on certified half marathon miles from governing bodies.
- Calibration: I set a bicycle counter on a steel tape calibration course per USATF procedures and I confirm temperature and tension ranges before rides.
- Measurement: I ride the shortest possible route twice with a Jones Counter and I record counts for each segment per RRTC protocol.
- SCPF: I add a 0.1 percent short course prevention factor to the layout so no runner covers less than the official distance if the line drifts.
- Verification: I submit maps, ride sheets, and calculations to the certifier and I receive a USATF certificate number with an expiration date.
- Governance: I match World Athletics road race standards and I reference USATF Course Measurement Manual and RRTC guidelines for methods.
Sources: World Athletics Competition Rules and Road Race Label regulations at WorldAthletics.org, USATF Course Measurement and Certification procedures at usatf.org and rrtc.net, NIST Special Publication 811 for unit conversions at nist.gov.
Why The Distance Matters For Training
I program sessions around 13.1 miles, because the body adapts precisely to the event load. I tie weekly volume, long runs, and taper plans to that fixed half marathon distance.
Building Weekly Mileage And Long Runs
I scale weekly mileage to support 13.1 miles without late fade.
- Run consistent weeks before adding pace work, for example 6–8 weeks of steady volume
- Run 25–35% of weekly mileage as the long run, for example 8–12 miles at peak
- Run most easy miles at conversational effort, then add blocks at goal half marathon pace in the final 4–6 long runs
- Run 5K segments at goal pace inside long runs, for example 2–3 x 5K with 1K easy between
- Run faster aerobic work on separate days, for example 4–6 x 1 mile at 10K pace with 2 minutes jog
I keep the 80–90% of total time easy and aerobic to protect recovery and raise durability, which aligns with polarized distribution evidence reported by Seiler and Kjerland 2006 and verified across endurance studies by Stöggl and Sperlich 2015. I anchor pace targets to physiological zones from Daniels’ Running Formula, 3rd ed., and I confirm event distance standards through World Athletics and USATF.
Numbers that map mileage to long run and pace focus:
| Experience level | Weekly mileage (mi) | Long run peak (mi) | Pace focus inside long run |
|---|---|---|---|
| Novice, first 13.1 | 20–30 | 9–11 | 2–4 miles at HM pace in final 3–4 long runs |
| Intermediate, recent 10K | 30–45 | 11–13 | 4–6 miles at HM pace, or 2 x 3 miles |
| Advanced, past HM | 45–65 | 13–16 | 6–8 miles at HM pace, or 3 x 3 miles |
I place key workouts at least 48 hours apart to maintain quality, as advised in ACSM guidelines on training stress and recovery kinetics.
Tapering And Recovery For 13.1 Miles
I taper to sharpen for 13.1 miles without losing aerobic gains.
- Cut weekly mileage by 20–30% 10–14 days out, according to Mujika and Padilla 2003
- Keep intensity with short HM pace strides and brief 10K pace reps, for example 6–10 x 30–60 seconds
- Trim long run to 60–75 minutes 7 days out, then 30–40 minutes easy 2–3 days out
- Maintain frequency, drop volume, limit new exercises to reduce muscle damage
I pursue recovery markers that track a half marathon load.
- Monitor resting heart rate and sleep duration daily, increase recovery when HR rises by 5–7 bpm for 2 mornings
- Replenish carbohydrates at 1.0–1.2 g per kg per hour for the first 4 hours post long run, per ACSM consensus 2016
- Rehydrate to 150% of body mass lost over 2–4 hours with electrolytes, per ACSM 2016
- Resume quality after 48–72 hours if muscle soreness ratings drop below 3 out of 10, based on DOMS time course literature
I base taper structure on meta-analytic data showing 2–3 week tapers with 41–60% volume reductions improve endurance performance, while preserving intensity, as summarized by Mujika and Padilla 2003 and updated reviews through 2018. I match these ranges to the fixed 13.1 mile target so race pace feels familiar on race day.
Measuring Your Runs Accurately
I track half marathon miles with tools that balance convenience and precision. I pair watch data with certified references to keep 13.1 miles honest.
GPS Accuracy And Mapping Tools
I log half marathon training with GPS then I verify distance when signal quality drops. I treat GPS as an estimate in urban canyons, heavy tree cover, or switchbacks.
- Select multi band GNSS for city routes, parks, and trails.
- Set recording to 1 Hz for steadier tracks on half marathon miles.
- Use auto lap at 1.00 mi for pacing, use manual lap at official markers during races.
- Cross check long runs on a certified route, use the USATF Course Search, Strava Global Heatmap, and municipal GIS maps.
- Export a FIT file, compare distance against a known segment of 5K or 10K.
I rely on open data for error context, then I plan routes that minimize signal issues.
Numbers at a glance
| Metric | Value | Source |
|---|---|---|
| GPS horizontal accuracy, open sky | 4.9 m median | GPS.gov, GPS Accuracy |
| Half marathon distance | 21,097.5 m | World Athletics, Road Race Manual |
| Mile to kilometer factor | 1.60934 km per mi | NIST, SI Brochure |
Example use cases
- Pick river paths, waterfronts, and tracks to reduce multipath on 13.1 miles rehearsal.
- Match splits to fixed landmarks, bridges, and trail posts at every 1.0 mi.
- Compare watch distance to a certified 5K loop, adjust pacing targets if drift exceeds 1%.
Treadmill And Track Calibration Tips
I validate indoor pace so my half marathon pacing stays consistent across environments.
Track calibration
- Run lane 1 for exact distances on workouts, use lane 2 only with conversion.
- Count laps for intervals, stack 12.5 laps for 5,000 m, stack 25 laps for 10,000 m.
- Apply lane math for accuracy on half marathon pace sessions.
Numbers for lanes
| Item | Value | Source |
|---|---|---|
| Standard track lap, lane 1 | 400.00 m | World Athletics, Facilities Manual |
| Standard track lap, lane 2 | 407.04 m | World Athletics, Facilities Manual |
| Extra per lap per lane | 7.04 m | World Athletics, Facilities Manual |
Treadmill validation
- Mark the belt with tape, count 100 revolutions, measure belt length with a tape, compute distance, compare console distance.
- Time a steady segment at 6.0 mph, 7.0 mph, and 8.0 mph with a stopwatch, compare expected distances of 1.00 mi in 10:00, 8:34, and 7:30.
- Use a calibrated foot pod for pace stability, match pod distance to a 1.00 mi indoor test.
I align treadmill pace to outdoor half marathon miles, then I anchor workouts to verified distances for race specific pacing.
Pace, Time, And Race Strategy For 13.1 Miles
I translate 13.1 miles into pace, time, and checkpoints. I match race strategy to the markers I used in training blocks.
Setting A Realistic Goal Pace
I set half marathon pace from recent data, then I confirm it in long workouts. I use one recent race, then I project with a standard model.
- Anchor with a recent race result, for example a 10K in the last 6 weeks
- Anchor with the Riegel model, pace_half = pace_recent × (distance_half ÷ distance_recent)^0.06 (Riegel, 1981)
- Anchor with threshold work, long tempo at 20–40 minutes near half pace confirms fit (Daniels, 2013)
- Anchor with course context, flat road differs from hilly or hot courses
I translate finish targets into exact paces, then I tape the line on my watch or bottle.
| Half marathon finish | Pace per mile | Pace per km |
|---|---|---|
| 1:30:00 | 6:52 | 4:16 |
| 1:45:00 | 8:01 | 4:59 |
| 2:00:00 | 9:09 | 5:41 |
| 2:15:00 | 10:18 | 6:24 |
| 2:30:00 | 11:27 | 7:07 |
I lock splits to familiar blocks, then I steer using 5K segments and the 6.55-mile halfway mark.
Negative Splits And Fueling Timing
I aim for a slight negative split, then I let terrain and weather set small adjustments. I run the first mile calm, then I settle into the goal rhythm by 5K.
| Segment | Target split guide |
|---|---|
| 0–5K | +5–10 sec per mile slower than goal pace |
| 5K–10K | Goal pace per mile stable |
| 10K–15K | Goal pace per mile steady, drift ≤3 sec |
| 15K–Finish | -5–10 sec per mile faster than goal pace |
I time fuel to the course, then I keep intake simple and repeatable.
- Take carbohydrate at 30–60 g per hour, for example 1 gel with 20–25 g every 30–35 minutes (ACSM, 2016)
- Take the first gel at 20–30 minutes, for example near the 3–4 mile aid station
- Take fluids to match thirst and conditions, for example 3–7 oz at aid stations every 2–3 miles (ACSM, 2016)
- Take sodium at 300–600 mg per hour in heat, for example sports drink plus 1 salt cap if sweat rate runs high (IOC Consensus, 2010)
- Take caffeine at 3 mg per kg 60 minutes pre race, for example 200 mg for a 150 lb runner if you use caffeine in training (ISSN, 2021)
I execute on landmarks I know, then I adjust only if heart rate or breathing spikes above my training ranges. Sources: World Athletics course standards, USATF certification guidelines, ACSM Position Stand on Nutrition and Athletic Performance (2016), IOC Consensus on sports nutrition (2010), Riegel performance model (1981), Daniels Running Formula (2013), ISSN Position Stand on caffeine (2021).
Common Misconceptions About Half Marathon Distance
I see the same myths every season about half marathon miles. I keep the facts tight so training and race strategy stay aligned.
“Is It Exactly Half A Marathon?”
A half marathon equals 21.0975 kilometers, which equals 13.1094 miles, which rounds to 13.1 miles. A marathon equals 42.195 kilometers by rule from World Athletics, so the half is exactly half of that standard. Course certification adds a Short Course Prevention Factor of 0.1 percent to the measured path to protect the minimum distance, not to make it longer for runners, per USATF and AIMS.
| Metric | Value |
|---|---|
| Marathon distance, km | 42.195 |
| Marathon distance, miles | 26.2188 |
| Half marathon distance, km | 21.0975 |
| Half marathon distance, miles | 13.1094 |
| Commonly stated half marathon distance, miles | 13.1 |
| Short Course Prevention Factor, percent | 0.1 |
Sources: World Athletics Technical Rules, USATF Course Measurement Procedures, AIMS Measurement Manual.
Variance Between Courses And Conditions
Course design and conditions can change what your watch shows, the official half marathon distance stays 13.1 miles.
- Expect small GPS variance on urban or tree covered routes, examples include 1 to 3 percent differences on watches from tall buildings or heavy canopy, per device documentation.
- Expect extra distance from wide lines and missed tangents, examples include 0.1 to 0.3 miles added when weaving or staying off the apexes on turns.
- Expect slower pace from elevation gain and headwinds, examples include hill segments and windy bridges, the course distance remains unchanged.
- Expect minor track or treadmill offsets from calibration, examples include treadmills reading 0.02 to 0.10 miles high or low without recent service.
- Expect chip timing to differ from gun timing on crowded starts, examples include 10 to 90 seconds of spread from corrals, the measured miles remain identical.
Sources: USATF Course Certification Guidelines, World Athletics Road Race Label Regulations, device manufacturer GPS accuracy notes.
Conclusion
You know what this effort asks of you and you have a plan. Trust your training trust your tools and keep your mind calm when the effort bites. Small steady choices add up to a strong finish.
I hope this guide helps you feel ready and clear headed. Take what fits your life and leave the rest. If you try something from here let me know how it goes. I am cheering for you and I believe you have more in you than you think.
Frequently Asked Questions
What is the official half marathon distance?
A half marathon is 13.1 miles, or 21.0975 kilometers. This standard is recognized by World Athletics and USATF. Certified race courses include a small safety margin so runners never run short of the official distance.
Is 13.1 miles exactly half of a marathon?
Yes. A marathon is 26.2 miles, so a half marathon is exactly 13.1 miles. The official metric distance is 21.0975 km, which is half of 42.195 km.
How do I convert 13.1 miles to kilometers?
13.1 miles equals 21.0975 kilometers. For quick math, use 21.1 km as a rounded value, but train with the exact figure for precise pacing and splits.
What’s the halfway point in a half marathon?
The halfway mark is 6.55 miles (10.54875 km). Use it to check effort and pacing, not to surge. Aim for smooth, even effort through this point to set up a strong finish.
How should I set a goal pace for a half marathon?
Base your goal pace on recent 5K/10K or tempo runs and long-run workouts. Use a realistic target you can hold for 13.1 miles, aiming for even pacing or a slight negative split.
What is a negative split and should I use it?
A negative split means running the second half slightly faster than the first. It’s a proven race strategy for half marathons, promoting control early and a strong finish if you pace smartly.
How do I structure weekly training for a half marathon?
Build a consistent base first. Then include one long run, one quality session (tempo or intervals), and easy miles. Beginners: 20–30 miles/week. Intermediate: 30–45. Advanced: 45–60+. Adjust for fitness and recovery.
How long should my long run be?
For most runners, 9–14 miles works. Beginners can build to 9–11 miles; experienced runners to 12–14 miles, occasionally including portions at goal half marathon pace to practice fueling and pacing.
What is tapering and how do I do it?
Tapering reduces mileage 1–2 weeks before race day to sharpen fitness. Cut volume by 20–40%, keep a touch of race-pace work, and prioritize sleep, hydration, and carbohydrate intake. Avoid adding new workouts.
How should I fuel and hydrate for a half marathon?
Consume 30–60g of carbs per hour. Take gels or chews every 30–35 minutes with water. Start well-hydrated, sip at aid stations, and adjust based on heat, sweat rate, and stomach comfort.
How can I use 5K segments and track laps for pacing?
Break the race into 5K blocks to check splits and effort. On a 400m track, 13.1 miles equals about 52.5 laps. Use laps or 5K splits in training to dial in even pacing.
How accurate are GPS watches for half marathons?
GPS is helpful but not perfect. Tall buildings, turns, and signal drift can add distance. Expect your watch to read long. Trust certified course markers and tangents over live GPS pace.
How are official half marathon courses measured?
USATF and World Athletics use calibrated bicycles and the Short Course Prevention Factor to ensure the course is not short. Multiple measurements and verification confirm the official 21.0975 km distance.
What is the Short Course Prevention Factor?
It’s a small safety margin added during certification to prevent courses from being short due to measurement error. This ensures every finisher covers at least the official half marathon distance.
Why might my race show more than 13.1 miles on my watch?
Common causes include running wide on turns, GPS inaccuracy, crowds, and course design. Certified courses meet or exceed the official distance; your device reading long is normal.
How should I monitor effort on race day?
Use pace, heart rate, and breathing rhythm. Start controlled, settle into goal pace by mile 3, hold steady through mile 10, then close slightly faster if you feel strong for a negative split.
How do I recover after a half marathon?
Rehydrate, eat carbs and protein within an hour, and sleep well. Easy movement, light stretching, and short recovery runs after 1–3 days help. Monitor heart rate and energy before resuming hard training.
How can I ensure treadmill and track workouts match outdoor pacing?
Calibrate your treadmill speed, use a foot pod if possible, and compare splits to a certified track (400m laps). Cross-check GPS runs on known routes to align indoor and outdoor paces.