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Estimate an AI cluster in this order: define the operating case, total every device’s input power, convert the electrical load to heat, apply facility overhead, choose a rack-density limit, then verify airflow or liquid-cooling delivery and the site’s electrical and structural constraints. A useful first-pass model is PIT = Σ device input watts, heat (BTU/h) = watts × 3.412, Pfacility = PIT × PUE, and rack count = ceiling(PIT ÷ allowable kW per rack). Treat the result as a design input for the electrical, mechanical and structural engineers, not as a purchase quantity based on GPU TDP alone.
The example below uses a 32-system DGX H100 scalable unit. NVIDIA’s planning figures put that unit at 326.4 kW of server-rack power, or 10.2 kW for each of 32 one-system rack footprints, before facility overhead. The same systems can be arranged as eight racks at 40.8 kW each when four systems share a rack. Your final design must use the exact server, network, storage and support-equipment specifications for your deployment.
1. Define exactly what the estimate includes
Write the boundary at the top of the worksheet before entering a number. “Power required” can mean IT equipment input at the rack, or the complete facility demand after UPS, distribution, cooling and other overhead. Mixing those boundaries is the fastest way to under-size a project.
Choose the operating case
| Case | What to record | How to use it |
|---|---|---|
| Expected operation | Typical input watts for the planned workload and utilization | Estimate energy use, operating cost and normal cooling load |
| Sustained training or inference | Measured or vendor-rated power while the cluster runs its intended long-duration workload | Size cooling and power for the load that can persist for hours or days |
| Peak or nameplate | Maximum credible simultaneous input, including startup or short-duration peaks where relevant | Set breakers, PDUs, conductors, thermal limits and protection settings |
State whether the calculation covers only servers and switches inside the data hall or also management, storage, cooling-distribution and electrical equipment elsewhere. Keep expected, sustained and peak columns separate; a single blended number hides the condition that controls each design decision.
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Record site assumptions
- Electrical service voltage, phase, frequency and available capacity.
- Allowable rack-kW limit from the power feed, cooling method, rack hardware and floor loading.
- Indoor temperature, humidity, altitude and the supply/return temperature targets.
- Required redundancy, such as N+1 or 2N, for UPS, generators, cooling units and distribution paths.
- Whether water, dry coolers or other heat-rejection equipment is available.
- Expansion positions and the date or phase in which they will be populated.
2. Build a complete bill of materials
Create one row per device or device class. Use vendor input-power data for both expected and peak columns and identify the document revision or model so a later hardware substitution does not silently invalidate the estimate.
| Equipment | Data to capture | Why it matters |
|---|---|---|
| GPU servers | Quantity, input watts, rack units, depth, inlet temperature range and power-cord arrangement | Usually the largest load and heat source |
| CPU, memory and local storage | Configuration-specific input power or a server-level value that includes them | GPU TDP excludes much of the host platform |
| Network and fabric switches | Port speed, optics, switch input watts and rack location | High-speed fabrics add continuous power and may require separate racks |
| Shared storage | Controller, drive-enclosure and expansion-shelf power | Storage can be a material load in training clusters |
| Management and service servers | Number and input watts | Often omitted from “GPU-only” estimates |
| Rack and power hardware | PDUs, busways, transfer switches and their losses | Include conversion and distribution losses inside the chosen boundary |
| Cooling support | CDUs, pumps, fans and controls | Include when these devices are part of the IT-room load or the facility budget |
Do not size from GPU thermal design power alone. CPUs, memory, fans, storage, networking, power-conversion losses and control equipment all consume power and produce heat.
3. Sum IT input power
For each operating case, add the input watts for every row:
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Keep a worksheet with at least three columns: expected, sustained and peak. If a vendor gives a range, preserve the range and use the upper credible value for protection and thermal design. Identify whether a value is per server, per rack or per scalable unit before multiplying it.
DGX H100 example
NVIDIA’s current DGX H100 SuperPOD planning guide lists 10,200 W EAP/EPP per DGX H100 system and notes that these systems operate at or near peak utilization continuously on AI workloads. For 32 systems:
32 × 10,200 W = 326,400 W = 326.4 kW
That is server-rack power for the scalable unit, not the final utility-service requirement. Network, storage, management and other infrastructure must be added if they are outside the 10,200 W figure.
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Document the multiplication
- Enter the quantity of each server and its applicable input-power value.
- Multiply quantity by watts and record the subtotal.
- Add switches, storage, management and support devices in their actual rack or room locations.
- Produce separate expected, sustained and peak subtotals.
- Have the equipment vendor confirm that the cited value includes the CPU, memory, fans and internal power supplies.
4. Convert electrical load to heat
Nearly all electrical power consumed inside the data hall eventually becomes heat. For a first-pass estimate:
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heat (BTU/h) = watts × 3.412
Use the maximum credible simultaneous IT load for thermal design, then apply the site’s environmental and redundancy rules. One DGX H100 system at 10,200 W corresponds to approximately 34,804 BTU/h of peak heat in NVIDIA’s planning guide. Thirty-two systems therefore represent about 1,113,728 BTU/h before additional equipment and facility losses.
Airflow calculation
NVIDIA’s DGX H100 planning material gives a minimum general airflow of 157 ft³/min (4.445 m³/min) per kW. It cautions that actual airflow changes with environmental conditions, altitude and component Delta T. Applying the planning minimum to 326.4 kW gives approximately 51,245 CFM, or 1,451 m³/min, for the server load. This is a screening value, not a substitute for a room airflow and containment calculation.
Verify supply airflow, return path, temperature rise, perforated-tile or grille capacity, containment and the effective capacity of CRAH or CRAC units. Short-circuiting supply air directly into returns can leave GPU inlets above their allowable temperature even when the room’s nameplate cooling tonnage appears sufficient.
Air-cooled rack planning values
Oracle’s current Capacity Requirements planning table uses 15 kW per rack and 150 CFM/kW for standard racks, and 17 kW or more per rack with at least 150 CFM/kW for specialty GPU/AI racks. These are early-design values that require product-specific confirmation; they are not universal limits for every server or facility.
| Planning category | Rack power value | Airflow value | Qualification |
|---|---|---|---|
| Standard rack | 15 kW | 150 CFM/kW | Early-design planning value; confirm with the product and site design |
| Specialty GPU/AI rack | 17 kW or more | At least 150 CFM/kW | Early-design planning value; dense hardware may require liquid cooling |
5. Convert IT power to facility demand
If the site’s power usage effectiveness (PUE) is known, estimate total facility power with:
Pfacility = PIT × PUE
For example, a 326.4 kW IT load at a stated PUE of 1.3 would be 424.32 kW of estimated facility power. That multiplication is valid only when the PUE definition and boundary match your calculation. PUE is a property of the site and operating condition, not a property of a GPU server.
The electrical engineer’s one-line design must then add UPS, transformer, distribution, generator and protection margins. Do not hide those margins in an unexplained percentage: show which equipment, redundancy mode and future phase each margin covers. Check both continuous current and short-duration or inrush behavior against breakers, PDUs and conductors.
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Choose an allowable kW per rack based on the actual power feed, cooling delivery, rack hardware and slab loading. Then calculate:
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rack count = ceiling(PIT ÷ allowable kW per rack)
Recalculate when storage, management or network racks are separate from compute racks. A compute-only division can undercount the physical racks and the cooling needed in adjacent rows.
DGX H100 layout alternatives
| Configuration | Systems per rack footprint | Rack power | System-rack count for 32 systems | Trade-off |
|---|---|---|---|---|
| Dense arrangement | Four | 40.8 kW | 8 | Fewer footprints, but substantially higher power density and more demanding cooling and floor loading |
| One system per rack | One | 10.2 kW | 32 | Lower rack density, but more floor area, aisles, cable runs and rack hardware |
The 326.4 kW total is the same in both arrangements; changing rack density changes delivery, serviceability and space, not the underlying server load.
7. Calculate floor space and structural requirements
Rack count multiplied by rack footprint is only the equipment footprint. Add the space needed to operate and expand the cluster:
- Cold aisles, hot aisles and containment structures.
- Front and rear service clearances required by the server and rack manufacturers.
- Cable pathways, overhead trays or under-floor routes, bend radius and cross-connect positions.
- Staging, spare-parts and fault-repair areas.
- Electrical rooms, UPS and distribution equipment.
- Cooling distribution units, manifolds, pumps, heat exchangers and maintenance bypasses.
- Unpopulated growth positions and safe access around them.
Confirm the slab’s distributed load and point-load rating for fully populated racks, not an average across the room. Dense GPU racks can exceed ordinary office or light-server assumptions. Account for the weight of batteries, liquid-filled CDUs, cable trays and containment when checking the structural design.
8. Choose and validate the cooling architecture
| Design | Required checks | Typical constraint |
|---|---|---|
| Air cooling | Supply and return airflow, temperature rise, containment, CRAH/CRAC capacity, grille or tile pressure and fan redundancy | Airflow and room distribution become limiting as rack kW rises |
| Direct-to-chip liquid cooling | CDU capacity, coolant flow, heat-exchanger approach temperatures, leak detection, maintenance bypass, hose routing and N+1 or 2N redundancy | Requires liquid distribution, controls, service procedures and heat rejection outside the rack |
For high-density liquid-cooled designs, NVIDIA’s 2026 DSX Facilities Infrastructure Reference Design specifies at least 1.5 LPM/kW of thermal-circuit flow and N+1 CDU redundancy for the cited generations. The same reference describes cabinet TDP from 198 kW to 330 kW. Treat those figures as requirements for the referenced designs, not as a rating for every future cabinet.
Align cooling capacity with the number of simultaneous operating loads (N), rather than simply the capacity of one power circuit. A circuit can be energized while the corresponding cooling path is unavailable, or multiple circuits can run together during training. Model those credible combinations and test failover.
9. Close the loop with site and network constraints
Before ordering equipment, reconcile the worksheet with the facility drawings and commissioning plan.
- Utility and electrical: Confirm service capacity, voltage, phase, transformer, breaker, PDU, UPS and generator ratings for the peak and redundancy cases.
- Heat rejection: Verify chilled-water, condenser-water, dry-cooler or other heat-rejection capacity at the design outdoor condition, not only at a mild-day rating.
- Water and leak control: For liquid cooling, confirm water quality, makeup or closed-loop operation, leak detection, isolation valves and safe maintenance bypass.
- Fire and life safety: Check suppression, detection, egress and any restrictions created by containment or liquid distribution.
- Noise and environment: Validate fan noise, vibration, temperature, humidity and altitude limits for the selected hardware.
- Network topology: Include fabric switches, optics, cable lengths, overhead paths and the distance limits of the chosen interconnect. A physically distant rack may require additional switches or optical equipment.
- Commissioning: Plan measurements of rack current, inlet and exhaust temperature, airflow or coolant flow, pressure, leak alarms and failover behavior under a representative workload.
10. A repeatable sizing worksheet
- List the boundary: write “IT input only” or “whole facility,” identify included rooms and state the expected, sustained and peak cases.
- Inventory every device: enter quantities, vendor input watts, rack units, dimensions, weight and connection requirements.
- Calculate three IT totals: sum expected, sustained and peak watts independently.
- Convert the peak: multiply watts by 3.412 for BTU/h and, for air systems, apply the applicable CFM/kW planning value.
- Apply PUE: multiply by the site PUE only when its boundary and operating condition are documented.
- Set density: select an allowable kW/rack that the power, cooling and slab can support; divide and round up.
- Lay out the room: place racks, aisles, containment, cable routes, electrical rooms, CDUs and growth positions.
- Check delivery: verify electrical current, airflow or coolant flow, temperature rise, approach temperatures and redundancy for simultaneous loads.
- Validate physically: obtain structural point-load approval and confirm utility, fire, water, noise and commissioning requirements.
- Recalculate after substitutions: repeat the worksheet whenever a server model, GPU configuration, switch, storage shelf or cooling component changes.
11. Common estimation failures and fixes
Using GPU TDP as the rack load
Symptom: the calculated kW is lower than the server’s input specification. Fix: use complete server input power and add networking, storage, management and conversion losses.
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Applying PUE to a partial boundary
Symptom: the facility number appears inconsistent with the utility or UPS design. Fix: document what the PUE includes and align the IT subtotal with that same boundary.
Counting only compute racks
Symptom: the floor plan has no room for fabric switches, storage, service access or cable turns. Fix: place every bill-of-material row on the plan and reserve growth positions.
Using nominal cooling tonnage
Symptom: rack inlets overheat while the room unit reports spare capacity. Fix: verify airflow paths, containment, temperature rise, tile or grille capacity and the cooling unit’s rating at the actual entering-water or entering-air condition.
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Symptom: the cluster passes normal operation but trips during failover or a second workload. Fix: model the maximum credible simultaneous load and the required N+1 or 2N state for both power and cooling.
Skipping structural checks
Symptom: a rack arrangement fits geometrically but exceeds slab point-load limits. Fix: submit populated rack weights, battery and CDU weights, and point locations to the structural engineer before installation.
12. Specify the physical equipment that makes the estimate measurable
A metered rack power distribution unit is the most direct measurement point for this workflow. Specify voltage, phase, receptacles, breaker rating, input connectors and the monitoring protocol to match the electrical one-line. Metering lets the commissioning team compare expected, sustained and peak worksheet values with actual rack current.
Dense deployments may require direct-to-chip liquid-cooling CDUs and high-density racks with hot-aisle containment. Select them by verified flow, heat-exchanger approach temperature, pressure, leak detection, bypass and redundancy requirements rather than by a headline kW rating. Availability and compatibility must be confirmed for the exact server generation and facility design.
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A defensible AI-cluster estimate is a traceable chain from device input watts to heat, facility power, rack count and usable floor area. Keep expected, sustained and peak cases separate; include every supporting device; use the site’s PUE only with a matching boundary; and validate airflow or coolant delivery against simultaneous and failure conditions. The 326.4 kW DGX H100 example demonstrates why two layouts with identical IT power can require very different rack counts, cooling systems and room footprints.
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