Transmission & Distribution (T&D) Line Loss Calculator
Not every watt of electricity generated reaches a paying customer. As power moves from a generator across the transmission network and down through the distribution system to end users, a portion is lost to resistive heating in conductors and transformers. The U.S. Energy Information Administration puts national average T&D losses at roughly 5% of electricity transmitted and distributed — and that lost energy was generated, paid for, and never delivered. This calculator converts energy generated (or delivered to the grid), a transmission loss rate, a distribution loss rate, and an electricity price into transmission losses, distribution losses, total T&D losses, the combined loss rate, the energy that actually reaches end customers, and the dollar value of what was lost. Pair it with our Reserve Margin / Capacity Adequacy Calculator for the resource-adequacy side of the same grid, our Transformer/Substation Sizing Calculator for the infrastructure that carries that power, and our analysis of why The Grid Is Nearing Its Limit.
Total energy generated and delivered to the transmission grid, in MWh.
Represents roughly 27% of total U.S. T&D losses (EIA/PNNL-based estimate).
EPRI's estimate for distribution-system losses specifically — roughly 73% of total U.S. T&D losses.
Price used to value the energy lost in delivery, in $/MWh.
energy generated × transmission loss rate (%)
energy after transmission × distribution loss rate (%)
transmission losses + distribution losses
In line with the ~5% U.S. national average T&D loss rate (EIA)
energy after transmission − distribution losses
total T&D losses (MWh) × electricity price ($/MWh)
Results update live as you type. For planning and field-check estimates — always verify against applicable standards and equipment ratings.
How we calculate this →Distribution losses outweigh transmission losses by nearly 3-to-1. Of the roughly 5% of U.S. electricity lost in delivery, EPRI attributes about 73% to the distribution network and only 27% to transmission — and a PNNL study found distribution transformers alone account for roughly a third of all T&D losses. On a system delivering 1 TWh a year, that's nearly $2 million in lost value annually at $40/MWh — electricity generated but never reaching a paying customer. It's also part of why proximity to generation matters: every mile of transmission and every step-down transformer between a power source and a large load adds another layer of loss.
How T&D line losses are calculated
Electricity is lost at two distinct stages as it travels from a generator to an end customer — first across the high-voltage transmission network, then through the lower-voltage distribution system that reaches individual premises. This calculator applies a sequential loss model: distribution losses are computed against the energy that remains after transmission losses have already been subtracted, not against the original generated energy. Six quantities tie the calculation together.
Transmission Losses (MWh) = Energy Generated / Delivered to Grid (MWh) × (Transmission Loss Rate (%) ÷ 100). The transmission loss rate reflects resistive (I²R) losses in high-voltage lines, substations, and step-up/step-down transformers; the default of 1.36% represents roughly 27% of total U.S. T&D losses per PNNL. At 1,000,000 MWh and 1.36%, transmission losses are 13,600 MWh. Energy After Transmission (MWh) = Energy Generated − Transmission Losses — 986,400 MWh at the defaults — the energy that reaches the distribution system.
Distribution Losses (MWh) = Energy After Transmission (MWh) × (Distribution Loss Rate (%) ÷ 100). Distribution systems operate at lower voltages and higher currents over a far larger, more granular network, which drives higher resistive losses; EPRI estimates distribution losses at roughly 3.64%, about 73% of total T&D losses. At 986,400 MWh and 3.64%, distribution losses are about 35,905 MWh. Energy Delivered to End Customers (MWh) = Energy After Transmission − Distribution Losses — roughly 950,495 MWh at the defaults — the energy that actually reaches paying customers.
Total T&D Losses (MWh) = Transmission Losses + Distribution Losses — about 49,505 MWh at the defaults. Total T&D Loss Rate (%) = (Total T&D Losses ÷ Energy Generated) × 100 — 4.95% at the defaults, in line with the ~5% U.S. national average reported by the EIA. Cost of Total Losses ($/yr) = Total T&D Losses (MWh) × Electricity Price ($/MWh) — roughly $1,980,200 at $40/MWh, the dollar value of energy generated but never delivered. Note that this is a simplified sequential model: real-world losses vary by voltage level, conductor size and age, loading, power factor, distance, and the number of voltage transformation steps along the path, and a PNNL study found distribution transformers alone account for roughly a third of all T&D losses. Data sources: EIA national average T&D loss rate (~5%, August 2025 Monthly Energy Review); EPRI distribution-system loss estimate (~3.64%); PNNL transmission vs. distribution loss split (27% transmission, 73% distribution); PNNL distribution transformer loss contribution (~one-third of total T&D losses).