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How to Measure 0-100 km/h with Your iPhone

You don't need an OBD dongle or a dedicated timing device. Your iPhone's GPS is accurate enough to measure acceleration times — here's how to do it properly.

Measuring your car's 0-100 km/h (or 0-60 mph) time used to require expensive equipment or a trip to a dyno. Now, GPS-based apps on your iPhone can do it with surprising accuracy — typically within 0.1-0.3 seconds of professional timing gear.

This guide covers how GPS acceleration timing works, how to get the most accurate results, and what to watch out for.

How GPS sprint timing works

Your iPhone's GPS chip updates its position multiple times per second. Sprint timer apps track these position changes to calculate speed over time. When you accelerate from a standstill, the app continuously measures your speed and records the exact moment you cross 100 km/h (or whatever target you set).

Modern iPhones (12 and newer) have dual-frequency GPS (L1 + L5), which improves accuracy significantly compared to older single-frequency models. Under good conditions (clear sky, no tall buildings), GPS speed is accurate within 1-2 km/h — more than enough for sprint timing.

What you need

  • An iPhone with GPS — Any iPhone works, but iPhone 12 or newer gives the best accuracy thanks to dual-frequency GPS.
  • A sprint timer app — Rovy has a built-in sprint mode that handles the timing automatically. Other options include Dynolicious and Dragy (which uses a separate GPS device).
  • A phone mount — A dashboard or windshield mount keeps your phone stable during hard acceleration. A phone sliding around on the seat isn't just inaccurate, it's unsafe.
  • A safe location — A straight, flat road with no traffic and good GPS visibility. Private tracks, airfield events, or closed courses are best.

Step-by-step guide

1. Mount your phone and wait for GPS lock

Secure your iPhone in a mount with a clear view of the sky (not under a metal roof or in a garage). Open your sprint timer app and wait for it to show a strong GPS signal. This usually takes 10-30 seconds.

2. Select your target speed

Most apps let you choose what you're timing: 0-100 km/h, 0-60 mph, 0-200 km/h, or custom intervals. In Rovy, you select this in sprint mode before starting.

3. Come to a complete stop

The timer starts when you begin moving, so make sure you're fully stopped. Some apps have a "ready" indicator that confirms you're at zero. Don't creep forward — a rolling start gives misleading results.

4. Accelerate

Floor it (safely). The app detects the moment you start moving and begins timing. It continuously tracks your speed until you hit the target. Keep accelerating past the target speed slightly — don't lift right at 100 km/h or the reading might miss the exact crossing point.

5. Review results

After you hit the target speed, the app shows your time. Most apps also display a speed-over-time graph so you can see how your acceleration curve looked. Do at least 3-5 runs and take the best consistent time (throw out any obvious outliers from wheel spin or GPS glitches).

Tips for accurate results

  • Clear sky matters — GPS accuracy drops significantly between buildings, under bridges, or in heavily wooded areas. Open sky = best results.
  • Flat road — Even a slight slope affects your time. Uphill makes you slower, downhill makes you faster. Run in both directions and average the times for a fair comparison.
  • Warm tires and engine — Cold tires have less grip. Do a few warm-up runs before your timed attempts.
  • Phone position — Keep your phone mounted high on the dash or windshield, not in a pocket or cupholder. Direct sky visibility matters for GPS accuracy.
  • Multiple runs — GPS timing has slight variance between runs. 3-5 attempts gives you a reliable number. If one run is way off from the others, it's likely a GPS hiccup.
  • Passenger weight — Extra passengers add weight and slow you down. For comparable results, try to run with the same load each time.

GPS vs. dedicated timing devices

Professional devices like the Dragy GPS meter or VBox use higher-frequency GPS updates (10-20 Hz vs. your iPhone's 1-5 Hz). This means they capture speed changes more precisely, especially during the initial launch where speed changes rapidly.

In practice, the difference is usually 0.1-0.3 seconds for a 0-100 km/h run. For casual testing and comparing your car against manufacturer specs, your iPhone is more than adequate. If you're tuning your car and need to measure the effect of small changes (like an exhaust upgrade), a dedicated device is worth considering. For more on how GPS speed measurement compares to your car's built-in speedometer, see our GPS Speed vs Car Speedometer breakdown.

What times to expect

For reference, here are typical 0-100 km/h times by car category:

  • Economy cars (Corolla, Golf): 9-12 seconds
  • Mid-range sedans (Camry, 3 Series): 6-8 seconds
  • Hot hatches (Golf GTI, Civic Type R): 5-6 seconds
  • Sports cars (Supra, Cayman): 4-5 seconds
  • Performance EVs (Model 3 Performance, Taycan): 3-4 seconds
  • Supercars (911 Turbo, AMG GT): 2.5-3.5 seconds

If your measured time is significantly slower than the manufacturer spec, don't worry — factory times are measured in ideal conditions (professional driver, prepped surface, optimal temperature). Real-world times on normal roads are typically 0.5-1.5 seconds slower.

Safety

Acceleration testing should only be done in safe, controlled environments. Never sprint on public roads with traffic, pedestrians, or intersections ahead. Track days, private roads, and organized events are the right places for this. Always obey local speed limits and traffic laws.

More from the blog

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Measure your 0-100 km/h with Rovy. Free on the App Store.

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