How Tesla Calculates Usable vs. Rated SOC and Range Estimates

Usable State of Charge (SOC)

Definition: Usable SOC is the battery percentage that reflects the usable energy available for driving, as displayed to the driver. In Tesla vehicles, the on-screen battery percentage corresponds to this usable state of charge, which excludes any energy reserves or buffers that the car keeps unavailable to protect the battery. In other words, 0% on the display is intended to mean the car is essentially out of usable energy (even though a small safety buffer remains). The purpose of using a “usable” SOC is to give the driver a realistic gauge of the energy that can actually be drawn for driving, without relying on the hidden buffer.

Inclusion of Degradation: Usable SOC inherently accounts for battery degradation over time. The battery management system (BMS) continually estimates the pack’s current nominal capacity, which tends to decline as the battery ages. The displayed SOC is calculated against this current capacity, not the original capacity when the car was new. This means that if your battery has lost (for example) 5% of its original capacity due to degradation, a “100%” charge now represents a smaller absolute kWh than it did when new. The car will show a lower full-charge range accordingly (while still displaying “100%” SOC), reflecting that reduced capacity. In practice, owners often gauge degradation by charging to 100% and noting the drop in rated miles – e.g. a Model 3 Long Range originally ~310 miles at 100%, now showing ~285 miles (about 92% of original, implying ~8% degradation). This happens because Tesla’s range display is linearly proportional to the battery’s capacity – the car uses the same fixed energy-per-mile value as always, so losing usable kWh directly reduces the miles shown. The usable SOC percentage itself still goes to 100% (since it’s relative to whatever the current full capacity is), but the car effectively “knows” the pack holds less energy, and that is reflected in the range number and in BMS readouts.

Inclusion of Temperature Effects: Tesla adjusts the usable SOC for temperature limitations. When the battery is very cold, a portion of the battery’s energy is temporarily unavailable (the infamous snowflake icon scenario). Tesla’s BMS calculates a “usable” SOC that excludes cold‑restricted energy. If your battery is cold enough to display a blue snowflake, you’ll notice a blue segment on the battery icon indicating the difference between the battery’s true state of charge and the temporarily usable portion. The lower end of that blue bar corresponds to the usable SOC (what you can actually draw), while the top of the blue region corresponds to the raw SOC including energy locked by cold. Tesla’s display already accounts for this – the range/percent shown omits the frozen portion, so you’re not misled by energy you can’t use until the pack warms. As the battery heats up (through driving, charging, or preconditioning), that blue region shrinks and the displayed range (and percent) “unlocks” additional miles in real time. In short, usable SOC is dialed down in cold conditions to reflect only the energy immediately available. Tesla’s official guidance notes that the blue snowflake means the battery is too cold to access full power or range, and that once warmed, the range will recover.

How It’s Computed: The Tesla BMS uses a combination of coulomb counting and voltage measurements to estimate the pack’s state of charge and capacity. Usable SOC is essentially calculated as:

In simpler terms, the car subtracts the fixed reserve buffer from both the “fuel tank” size and the remaining “fuel” to get the usable fraction. Here Nominal Full Pack is the BMS’s latest estimate of total pack energy (at 100% charge) and Nominal Remaining is the current energy in the pack. The Energy Buffer is a small amount (several kWh) that is not counted in the displayed 0–100% (it’s held in reserve below “0%” and sometimes above “100%” for calibration). By using the usable values (subtracting that buffer), the car shows 0% when you hit the reserve and tries to make “0 = 0” (so 0% really means essentially empty). For example, if the BMS thinks your pack holds 70 kWh now and reserves ~3 kWh as buffer, it will treat ~67 kWh as 100% usable. If 33.5 kWh are left (plus buffer), it will display ~50%.  

Rated State of Charge (SOC)

Definition: “Rated” SOC (or more commonly, Rated Range) refers to the distance the car can travel on its remaining charge under standardized conditions (specifically the EPA test cycle or equivalent). Instead of a percentage, it’s the range-in-miles (or km) display that Tesla shows if you toggle the battery from % to distance. This number is often called “Rated Range” because it’s pegged to the car’s official EPA-rated range efficiency. In essence, the car converts the usable energy remaining into a mileage estimate by assuming you’ll drive with the same efficiency that was used to rate the car’s range when new. Many owners keep the display in miles/km, which reads out this rated range figure.

Tesla Mileage Estimations

Tesla gives drivers two types of range estimates: (a) the EPA-rated range (the default shown as “miles/km remaining”, discussed above) and (b) projected range based on recent consumption (available via the Energy app or navigation predictions). Understanding both is key to knowing how far you can really go.

EPA-Rated Range (Label Range)

This is the official range figure derived from standardized EPA tests, and it underpins the rated miles on the display. Definition & Calculation: The EPA-rated range is determined by running the car through a prescribed set of driving cycles on a dynamometer, measuring energy use, and then extrapolating how far the car would go on a full charge. The EPA’s procedure isn’t a single constant-speed run – it’s a combination of city and highway profiles. In fact, the EPA range is a weighted composite: about 55% city cycle and 45% highway cycle, with adjustments for real-world factors. The city test (UDDS) involves lower speeds and stop-and-go, which EVs handle efficiently, and the highway test (HWFET) reaches about 60 mph max (average ~48 mph). Because real highway driving is often 70+ mph, the EPA adds a 30% energy consumption penalty to the raw highway results (“aggressive driving and HVAC” factor) to better reflect driving at higher speed and using climate control. After running these cycles, the measured energy consumption (in Wh/mi) is applied to the vehicle’s usable battery capacity to compute the range. In practice, automakers often do a 5-cycle test or apply a correction factor to 2-cycle results to arrive at the label range. For example, if a car uses ~300 Wh/mi on EPA’s combined test and has ~75 kWh usable, it would get about 250 miles. These tests assume moderate climate (around 20–25°C/68–77°F), no significant elevation change, and no accessories like A/C or heat beyond the standardized usage included in the test cycles. Assumptions: The EPA cycles are relatively gentle – e.g., the highway cycle’s ~48 mph average is lower than typical interstate speeds, and it has no extreme cold/hot weather usage beyond the default climate settings in the test. Thus, the EPA-rated range represents an optimistic but achievable scenario. It’s essentially the “ideal” range under mixed driving at moderate speed and temperature.

Tesla uses this EPA result to set the car’s rated consumption constant. Notably, Tesla sometimes software-limits power or uses other tricks during EPA testing to maximize the number, and historically they have aligned the in-car range display to match the EPA value including some of the buffer. This led to cases where drivers observed that if you drive a Tesla at a steady 65–70 mph on flat ground, you might not hit the full EPA range – because the test weighting skews a bit more city driving, and real highways are faster than the EPA’s simulation. Consumer reports and independent tests have often found Tesla (and other EVs) falling short of EPA range in real-world highway use, which is more a reflection of the EPA’s test methodology than a unique Tesla issue. The bottom line is that EPA range is a standardized metric. It’s great for comparing vehicles and for a rough idea of capability, but real-world range will vary with conditions. Tesla’s rated miles stick to that EPA yardstick: it’s a fixed benchmark, not a dynamic estimate of how far you will get on your next drive if conditions differ.

Projected Range (Energy App & Real-Time Estimations)

Tesla provides a more context-aware range estimate through the Energy app (and via the navigation system’s predictions). This is often called projected range or estimated range, and it takes into account your recent efficiency and other factors to predict how far you can go with the remaining charge.

Calculation Method: The simplest form of projected range is found in the Consumption tab of the Energy app on the car’s touchscreen. Here, Tesla allows you to choose an averaging window (e.g. last 5, 15, or 30 miles – or 10, 25, 50 km) and then calculates how many miles you can drive if your future consumption matches your past consumption over that window. In effect, the car knows “you have X kWh usable remaining” and it knows “you’ve been using Y kWh per mile recently,” so it computes Remaining miles = X / (Y per mile). This appears as the projected range on that screen. For example, if over the last 30 miles you averaged a very efficient 200 Wh/mi and you have 50 kWh left, the projected range would be 50 kWh ÷ 0.200 kWh/mi = 250 miles. If instead you were driving fast and averaged 300 Wh/mi, that same 50 kWh would project only ~167 miles. The driver can see this in real time: the Energy chart shows a colored line for your actual energy usage vs a gray line for the rated baseline, and at the bottom it will list “Projected range: ___ miles” based on the selected averaging period. Tesla’s official description notes that projected range is calculated using remaining battery energy and your average consumption over the chosen distance. You can even toggle between “Instant” range (which uses only the last few minutes of data for a quick projection) and “Average” range (which uses the longer selected window). The Average projected range over 10/25/50 km is considered the most realistic indicator for your current trip since it smooths out short-term fluctuations. In summary, this Energy app projection is highly responsive to your driving – drive more efficiently, it will go up; drive inefficiently, it will plummet, reflecting the reality of your consumption.

Factors Influencing Projected Range: Recent driving efficiency is the primary factor – anything that affects energy usage in the last few miles affects the projection. This includes your speed, acceleration pattern, terrain, climate control use, and more. For instance, terrain (e.g. hills) has a huge effect: if you just climbed a mountain, your recent Wh/mi will be very high and the projected range will look terrible – even though if the road ahead goes downhill, you’ll do much better than the projection. Conversely, after a long gentle descent (very low Wh/mi), the projection might be overly optimistic if an uphill is coming. The car’s basic consumption projection doesn’t know what’s ahead (unless you use navigation), so it just extrapolates recent conditions. Climate usage is another big one: running the cabin heater or A/C draws additional power from the battery. This is reflected in your recent Wh/mi. For example, in winter, running the heater at full blast while driving in stop-and-go traffic can push consumption way up (perhaps 400+ Wh/mi in a Model 3). The projected range will incorporate that – showing a much shorter range than rated. If you then turn off the heater, your Wh/mi will drop and after a while the projected range will start to improve as the average consumption falls. Likewise, extreme temperatures affect range: cold weather not only increases drivetrain and air resistance losses, but the battery itself may need heating. All that is captured in the higher Wh/mi. The projection will thus be lower on a cold day if you’ve been using energy to heat the battery and cabin. Battery condition (temperature and state) also comes into play. If the battery is cold, aside from the blue locked portion (which we discussed under usable SOC), the car uses energy to warm it. This can make your recent consumption look worse than normal. Once the battery warms, consumption efficiency improves. So, if you start driving with a cold pack, the initial projected range might be very low (because you’re spending a lot of energy on heating and have reduced regenerative braking), but after some time the projection can recover. Importantly, when the battery is cold the car already reduced the available energy in the calculation (locked some away), so the remaining X kWh used for projection is only the unfrozen portion. As the pack warms and that extra energy becomes usable, the X increases and effectively extends range. A driver will see the projected miles creep up as the blue snowflake goes away.

Dr.EV Battery Level and Mileage

Battery Level (SOC): Active Degradation Adjustment: Continuously updates SOC based on real-time battery health (State of Health, SOH), clearly reflecting current battery capacity.

Mileage (Range Estimations): Real-World Efficiency: Combines recent driving efficiency metrics with real-time battery health data to calculate mileage.