Sharing an EV Charger in an Apartment Building: The Weekly Math

Most people think shared EV charging in an apartment building is a scheduling problem. But actually, it’s an arithmetic problem. The question isn’t “how do we take turns?” — it’s “does the charger have enough hours in the week to deliver the kilowatt-hours everyone needs?”

Once you frame it that way, the answer stops being a guess. You can calculate it, and you can tell within an afternoon whether one shared Level 2 charger will cover your building or whether you need two. If you’re earlier in the process and just trying to figure out whether an EV fits your life at all, the EV Readiness Check walks through the broader question first.

Start with weekly demand, not parking spots

A single EV’s weekly electricity demand depends on three things: how many miles the driver covers, how efficient the car is, and how much of that charging happens at the shared charger versus elsewhere (workplace, DC fast chargers, visiting family).

Here’s the math for a few common vehicles, assuming a typical 200 miles per week:

That’s the energy that has to reach the battery. But because Level 2 charging is only about 90% efficient grid-to-battery (per our own readiness engine), the meter actually records about 11% more. A Model 3 driver pulls roughly 54 kWh from the wall; a Lightning driver pulls closer to 101 kWh.

Now count the hours the charger actually has

A standard shared Level 2 charger in a multi-family building runs at 7.7 kW (32 amps on a 40-amp circuit). The week has 168 hours. In theory, that’s 168 × 7.7 = 1,294 kWh of deliverable energy. But nobody runs a shared charger 24/7.

The ESIG EV Load Forecasting Guide gives a planning range of 25–40% daily port utilization for multi-family Level 2 chargers. At the top of that range, you’re looking at roughly 67 hours of charging per week, or about 516 kWh delivered. At the middle (32%), it’s closer to 54 hours and 415 kWh.

So the realistic weekly budget of a single shared 7.7 kW Level 2 charger is somewhere around 400–500 kWh of billed energy per week. That’s the number you divide into.

The division: how many EVs fit?

Take 450 kWh/week as the planning midpoint. Now divide by per-vehicle demand:

This lines up with the ESIG guide’s planning range of 3 to 6 vehicles per shared port in multi-family housing. The sedan buildings are at the top of the range; the truck-heavy buildings are at the bottom. If your building is adding a mix of pickups and SUVs, plan for the low end.

The ESIG session planning data suggests multi-family Level 2 users typically plug in 2–4 times per week for 4–8 hours per session — which is consistent with the math above. One long overnight plus one weekend top-up covers most sedan drivers.

Why you should not trust the top of these ranges

Here is something the planning guides do not point out about their own numbers: the three multi-family ranges do not reconcile with each other. Run them at their maximums and you get an impossible building.

Take 6 vehicles per port, each charging 4 times a week, each session lasting 8 hours. That is 6 × 4 × 8 = 192 hours of charging demand. A week contains 168 hours. The port would need to be occupied 114% of the time — which is not a tight building, it is an arithmetic impossibility.

Run the midpoints instead — 4 or 5 vehicles, 3 sessions each, 6 hours per session — and you get 81 hours a week, or 48% utilization. That is still well above the 25–40% band the same guide publishes. Only near the bottom of every range do the three figures agree: 3 vehicles, 2 sessions, 4 hours each is 24 hours a week, or 14% utilization, which sits just under the published band.

The practical lesson for a resident is simple. These are planning ranges written for utilities sizing infrastructure, not promises about your parking garage. When a property manager says the guidance supports six cars per charger, they are quoting a number that only works if nobody drives much. Size your expectations from the bottom of the range, not the top, and treat anything above four vehicles per port as needing a scheduler to function.

Where the math breaks

The weekly budget assumes two things that don’t always hold.

Peak-hour collision

If everyone plugs in at 6pm when they get home, you don’t have 54 hours of availability — you have four people fighting over the same four-hour window. Sessions back up. People get skipped. The charger might sit idle from 2am to 7am because the last person unplugged at midnight and the next won’t arrive until the morning.

This is a scheduling problem the arithmetic can’t solve on its own. Buildings that make shared charging work usually have either an app-based scheduler (ChargePoint, Blink, EV Connect) or an informal signup sheet. Without one, the ceiling drops from 5–6 vehicles to about 3.

Long-dwell parking

A full charger is only useful if people unplug when they’re done. A car that sits plugged in for 36 hours while the driver is at work takes up a slot that could have served two other vehicles. Most shared systems address this with idle fees (ChargePoint charges after the session completes), but the fee only works if people get the notification and move the car. In practice, this is the single biggest reason shared chargers underperform their theoretical capacity.

A real example: Jamie’s building

Jamie went through the typical gradual transition — Prius, then Volt, then Bolt, now an Equinox EV. The Equinox lives in a 40-unit apartment building that added two shared Level 2 chargers two years ago. Four EVs regularly use them. One is Jamie’s Equinox (~50 kWh/week), two are Model Ys (~60 kWh/week each), and one is a Lightning (~100 kWh/week).

Weekly demand: about 270 kWh. Weekly capacity across two chargers at the ESIG mid-range: about 830 kWh. Plenty of headroom — but the building still sees occasional conflicts because the Lightning owner tends to plug in Friday evening and leave the truck connected until Sunday morning. The arithmetic is fine; the behavior isn’t.

That’s the pattern. One shared charger covers 3–6 households on paper. In practice, you need either strong norms, idle fees, or a scheduler to hit the top of that range. If you’re evaluating a building for EV ownership, there are more scenarios worth working through in our Apartment & Tenant EV Guide, and if you’re already running the two-EV version of this problem at home, this breakdown on sharing one charger between two cars covers the same math at smaller scale.

When a shared port will not work for you personally

Everything above sizes the charger for the building. The more useful question is whether it works for you specifically, and there are three cases where the honest answer is no.

The first is simple arithmetic about your share. A 450 kWh weekly budget split across five drivers gives you about 90 kWh. If your own demand is much past a quarter of the building’s budget — a little over 400 miles a week in an efficient sedan, or about 220 miles a week in a full-size pickup — you are not one of several drivers sharing a port. You are the reason the port is full, and your neighbours will notice before the building does.

The second is timing rather than volume. A shared charger assumes you can move your session. If you work nights, leave before six, or cannot reliably come down to unplug and swap the car, the 4–8 hour session the planning data assumes never happens for you. Flexibility, not kilowatt-hours, is what shared charging actually costs you.

The third is that you need the car charged on a schedule you do not control. If being unable to charge on a given night would genuinely strand you the next morning, a shared port is a convenience, not infrastructure. In that situation, plan around workplace or public charging as your primary source and treat the building’s charger as a bonus when it happens to be free.

When one charger isn’t enough

You’ve outgrown a single shared Level 2 charger when:

At that point, the building has three options: add a second Level 2 charger (if the panel can support another 40-amp circuit, which requires a load calculation by a licensed electrician), add a lower-power Level 2 on a smaller circuit, or route some drivers to workplace or public charging. If you want to see what the US Department of Energy says about multi-family planning specifically, the Alternative Fuels Data Center has a good overview, and the DOE’s best practices for EV charging at multi-unit dwellings covers the governance and cost-recovery side.

If you want to work the math for your specific situation — your mileage, your vehicle, your realistic access to a shared port — the readiness tool runs the full calculation and tells you whether the shared setup is enough or if you need a backup plan.

Frequently asked questions