Jul 29, 2026 · cs.LGJ/K move · Enter open · S save
Tina Vartziotis, Rodopi Kosteli, Elli Vartziotis, George Dasoulas+4
1National Technical University of Athens, Patission Complex 42, 10682 Athens, Greece · 2Harvard University, 1350 Massachusetts Avenue, 02138 Cambridge, MA, USA · 3TWT GmbH Science & Innovation, Industriestraße 6, 70565 Stuttgart, DE · NIKI Ltd Digital Engineering, 205 National Resistance Street, 45500 Ioannina, Greece · 6National and Kapodistrian University of Athens, Panepistimiou 30, 106 79 Athens, Greece
The operational energy consumption of large language model (LLM) inference is becoming an increasingly important component of the environmental footprint of deployed AI systems. However, direct measurement of inference energy often requires hardware telemetry, power instrumentation, or infrastructure-specific monitoring, limiting its applicability in comparative studies, early-stage system design, and sustainability reporting. This report presents an analytically structured, empirically calibrated, GPU-level methodology for estimating LLM inference energy on NVIDIA H100-class accelerators without direct runtime measurement. The proposed estimator combines parameter-scaled transformer FLOP accounting, calibrated memory-traffic factors, and hardware-specific energy coefficients for FP16/BF16 tensor-core computation and high-bandwidth-memory movement. It explicitly separates prompt prefill from autoregressive decoding, enabling energy estimates for input tokens, output tokens, and complete inference requests. The methodology further decomposes total energy into compute, parameter-access, key-value-cache write, and attention-read components, allowing the scaling behavior with model size, context length, and generated-token count to be analyzed. The resulting estimates are not intended to replace physical power measurements; rather, they provide transparent, reproducible, and assumption-explicit approximations suitable for model comparison, green-coding analysis, and design-time evaluation of LLM inference workloads.