DC Fast Charger Sizing Calculator
Sizing a DC fast charging site is really two problems stacked together: how many stalls you need to serve the traffic, and how much electrical service those stalls demand from the utility. This calculator takes your expected daily vehicle volume, the average energy each session adds, the charger power rating, the number of stalls, the site's operating hours, and a simultaneity/diversity factor, then reports the average session duration, the total daily charging-hours the traffic requires, the stall utilization rate that results, the total connected charger capacity, and the realistic site peak electrical demand. For the broader load across a mixed fleet of charger types (Level 1, Level 2, and DC fast together), see our Charging Station Load Calculator; and once you know your site peak demand, the Transformer/Substation Sizing Calculator helps size the upstream electrical infrastructure that has to be sized and approved by the utility.
Average number of EVs you expect to charge at the site each day.
Typical DC fast charging sessions add roughly 30-60 kWh per stop, depending on vehicle battery size and how depleted it was on arrival.
Selecting a rating auto-fills the power value below (still editable). 50 kW is an older standard; 150 kW is common today; 350 kW is the current high-power tier.
The rated power output of each DC fast charger at the site.
How many individual DC fast charging stalls (dispensers) the site has.
How many hours per day the site is open and available for charging.
The percentage of connected charger capacity actually drawn at once during peak usage -- not every stall runs at full rated power simultaneously.
(average energy added per session ÷ charger power rating) × 60
(expected vehicles per day × average session duration) ÷ 60
(total daily charging-hours ÷ (stalls × operating hours)) × 100
number of charging stalls × charger power rating
total connected charger capacity × simultaneity/diversity factor
Results update live as you type. For planning and field-check estimates — always verify against applicable standards and equipment ratings.
How we calculate this →A single 150 kW DC fast charger can fully recharge a typical EV's usable range in under 20 minutes, but that speed comes with real electrical infrastructure costs. A 6-stall, 150 kW site has 900 kW of connected charger capacity -- roughly the same order of magnitude as a mid-size commercial building's total electrical service -- even though a realistic simultaneity factor brings actual peak demand down to around 540 kW. Getting that site connection sized and approved by the utility is often the longest lead-time item in a charging station project, not the charging equipment itself.
How DC fast charger sizing is calculated
This calculator ties the operational sizing of a DC fast charging site (how many stalls you need to serve the traffic) to its electrical sizing (how much utility service those stalls demand). Five quantities tie the calculation together.
Average Session Duration (minutes) = (Average Energy Added per Session (kWh) ÷ Charger Power Rating (kW)) × 60. This is how long a single charging session lasts if the charger delivers its full rated power throughout; at 40 kWh and 150 kW, that is (40 ÷ 150) × 60 = 16 minutes. Real sessions taper as the battery fills (most EVs reduce charge rate above ~80% state of charge), so treat this as a best-case planning figure.
Total Daily Charging-Hours Required (charger-hours/day) = (Expected Vehicles per Day × Average Session Duration (minutes)) ÷ 60. This converts the per-session time into the total charger-occupancy hours the daily traffic generates across all stalls; at 50 vehicles and 16 minutes each, that is (50 × 16) ÷ 60 = 13.33 charger-hours/day.
Stall Utilization Rate (%) = (Total Daily Charging-Hours Required ÷ (Number of Charging Stalls × Operating Hours per Day)) × 100. This is the share of available stall-hours actually consumed by charging, and the key indicator of whether the stall count is right-sized; at 13.33 charger-hours across 6 stalls running 18 hours (108 available stall-hours), that is (13.33 ÷ 108) × 100 = 12.3%. A low rate means room for traffic growth before more stalls are needed; a rate approaching 100% means vehicles will queue.
Total Connected Charger Capacity (kW) = Number of Charging Stalls × Charger Power Rating (kW); at 6 stalls and 150 kW, that is 900 kW of nameplate capacity installed on site. Site Peak Electrical Demand (kW) = Total Connected Charger Capacity × (Simultaneity/Diversity Factor (%) ÷ 100); at 60%, 900 kW becomes 540 kW of realistic peak demand -- the figure the utility service, transformer, and feeder must be sized to deliver. The simultaneity factor matters because not every stall draws its full rated power at once: vehicles arrive at different times, charge at tapering rates as batteries fill, and sit idle between sessions. Sizing service to the full connected capacity of every charger would significantly oversize (and overpay for) the utility connection. Utilities and interconnection studies care about peak coincident demand, not average draw, so service requests should be sized from peak. Data sources: DC fast charger power ratings and charging time data from EV charging equipment manufacturers (Tesla Supercharger, Electrify America, EVgo, ABB, others); EV battery sizes and fast-charging energy additions from vehicle specifications; electrical load diversity factors from utility interconnection standards (IEEE 1547, NEMA); charging station design practices from EVSE industry guidelines.