Engineering Reference Library

W	Watts (apparent power)
V	Voltage (Volts)
A	Amperage (Amps)

Power Calculator

√3	1.732 (phase constant)
208V / 30A	10.8 kW apparent
208V / 60A	21.6 kW apparent
400V / 32A	22.2 kW apparent

Power Calculator

For continuous loads (defined as >3 hours), the NEC (Article 210.20) requires that the load not exceed 80% of the branch circuit rating. Servers are always continuous loads.

20A circuit	16A safe / 3.84 kW @ 240V
30A circuit	24A safe / 5.76 kW @ 240V
60A circuit	48A safe / 11.5 kW @ 240V

Power Calculator

Used to size CRAC/CRAH cooling units. Always calculate heat output from total rack draw, not just server TDP — include switches, PDUs, and patch panels.

5 kW rack	17,060 BTU/hr
10 kW rack	34,120 BTU/hr
20 kW rack	68,240 BTU/hr

PUE 1.0	Theoretical perfect — impossible
PUE 1.2	Excellent (hyperscale target)
PUE 1.5	Average enterprise DC
PUE 2.0+	Aging / inefficient facility

120V 1φ	US standard office / NEMA 5-15
208V 1φ/3φ	US data center standard
230V 1φ	EU / international standard
400V 3φ	High-density EU / hyperscale
480V 3φ	US high-density / industrial

U	Usable capacity
S	Single drive size
n	Total drive count
p	Parity drives (overhead)

RAID Calculator

RAID 0	No fault tolerance, penalty ×1
RAID 1	1 drive failure, penalty ×2
RAID 5	1 drive failure, penalty ×4
RAID 6	2 drive failures, penalty ×6
RAID 10	50% overhead, penalty ×2

RAID Calculator

R / W	Read % / Write % (decimal)
T	Total raw IOPS pool
P	RAID write penalty

IOPS Calculator

7.2K SATA HDD	~75–100 IOPS
10K SAS HDD	~130 IOPS
15K SAS HDD	~175–210 IOPS
SATA SSD	~5,000+ IOPS
SAS SSD	~15,000 IOPS
NVMe SSD	~10K–1M+ IOPS

IOPS Calculator

D	Data size (bytes)
S	Link speed (bytes/sec)
η	Efficiency factor (typically 0.8)

80% efficiency accounts for TCP overhead and background traffic on shared networks. Production windows rarely sustain 100% line rate.

Backup Calculator

Drive manufacturers use base-10 (1 TB = 1,000,000,000,000 bytes). Operating systems use base-2 (1 TiB = 1,099,511,627,776 bytes). A "12TB" drive formats to ~10.9 TiB.

1 TB (decimal)	≈ 931 GiB
12 TB drive	≈ 10.9 TiB usable
Loss factor	~7.4% per TB

n	CIDR prefix length
−2	Network + Broadcast reserved

Subnet Calculator

/8	16,777,214 hosts
/16	65,534 hosts
/24	254 hosts — standard LAN
/25	126 hosts — split subnet
/26	62 hosts
/28	14 hosts — small segment
/29	6 hosts
/30	2 hosts — point-to-point

Subnet Calculator

Network speeds are in bits; storage is in bytes. Divide by 8 to convert.

1 Gbps	~125 MB/s theoretical max
10 Gbps	~1.25 GB/s theoretical max
25 Gbps	~3.125 GB/s theoretical max
100 Gbps	~12.5 GB/s theoretical max

10.0.0.0/8	Class A — 16M addresses
172.16.0.0/12	Class B — 1M addresses
192.168.0.0/16	Class C — 65K addresses

These ranges are non-routable on the public internet and are reserved exclusively for private network use.

C	Total core count
Hz	Clock speed (GHz)
IPC	Architecture factor
η	Cache efficiency multiplier

CPU Calculator

<1 MB/core	Dense / VDI — memory pressure expected
1–2 MB/core	General enterprise — adequate
>2 MB/core	Enterprise target — recommended minimum
>4 MB/core	Performance — ideal for DB workloads

CPU Calculator

P	Model parameters (billions)
B	Bytes per param (precision)
U×T×C	KV cache (users × tokens × 0.00035)

Apply a 1.2× overhead multiplier for CUDA kernels and activation tensors.

GPU Calculator

FP32	4 bytes/param — Training
BF16/FP16	2 bytes/param — Full quality inference
INT8	1 byte/param — Minimal quality loss
INT4/GPTQ	0.5 bytes/param — Aggressive quant

Rule of thumb: a 7B FP16 model requires ~14 GB VRAM before overhead.

GPU Calculator

RTX 4090	24 GB GDDR6X — prosumer
L40S	48 GB — inference / VDI
A100	80 GB HBM2e — enterprise AI
H100 SXM	80 GB HBM3 — data center AI
H200	141 GB HBM3e — LLM scale

GPU Calculator

2:1	Conservative — latency-sensitive apps
4:1	Standard — general enterprise VMs
8:1	VDI / test environments
10:1+	Dev / bursty — monitor carefully

Physical thread count = cores × 2 (SMT/HT). Always size N-1 for high availability.

1U = 1.75 inches (44.45mm). Defined by EIA-310. Standard racks are 42U; half racks are 22U. Open-frame telco racks are often measured in inches.

1U	1.75" — thin switches, 1U servers
2U	3.5" — standard enterprise server
4U	7" — GPU chassis, storage heads
10U	17.5" — storage JBODs

Rack Calculator

Tier I	99.671% — basic, no redundancy
Tier II	99.741% — partial redundancy
Tier III	99.982% — concurrent maintainable
Tier IV	99.995% — fully fault tolerant

Tier III allows 1.6 hrs downtime/year. Tier IV allows ~26 minutes/year.

ASHRAE TC 9.9 Class A2 covers most enterprise IT equipment.

Inlet Temp	10°C – 35°C (50°F – 95°F)
Humidity	8% – 80% RH non-condensing
Dew Point	≤ 21°C
Recommended	18°C – 27°C inlet (64°F – 80°F)

RPO	Recovery Point Objective — max acceptable data loss (time)
RTO	Recovery Time Objective — max acceptable downtime duration

Example: RPO 4hr + RTO 2hr means you can lose up to 4 hours of data, and must be back online within 2 hours of declaring a disaster.

Backup Calculator

These three figures are often confused during power budgeting:

Nameplate	PSU max rating — always highest
TDP	Vendor thermal design ceiling
Actual Draw	Real-world idle to peak (50–80% of TDP typical)

For conservative planning, use nameplate. For realistic sizing, use vendor-provided SPECpower data.

IP ratings define enclosure protection against dust and water. Relevant for edge and outdoor deployments.

IP20	Finger-safe, no water protection
IP44	Splashproof — indoor/semi-exposed
IP54	Dust-resistant, splashproof
IP65	Dust-tight, low-pressure water jet
IP67	Dust-tight, temporary immersion