How this calculator works

The working class of a crane is determined by two independent factors defined in ISO 4301-1:2016 and GB/T 3811: how often the crane works (utilization class U) and how heavily it is loaded (load state Q). The calculator combines both to give the working class A.

Step 1 — Total work cycles → utilization class U

A work cycle starts when you begin lifting a load and ends when you are ready to lift the next one. The total number of cycles over the crane's design life determines the utilization class:

N = years × 270 days × hours/day × (60 ÷ minutes per cycle)

Working days are standardized to 270 per year. N is compared against the U0–U9 thresholds (see the Utilization classes tab).

Step 2 — Load spectrum → load state Q

The load spectrum factor Kp measures how heavily loaded your cycles are. Each load level contributes with the cube of its ratio to rated capacity — this reflects how fatigue damage scales with load:

Kp = Σ [ (nᵢ / N) × (Gᵢ / Gmax)³ ]

nᵢ/N = share of cycles at load level i · Gᵢ/Gmax = that load as a fraction of rated capacity. Kp ≤ 0.125 → Q1 · ≤ 0.25 → Q2 · ≤ 0.5 → Q3 · > 0.5 → Q4.

Step 3 — Look up working class A

The U class and Q state cross-reference in the working class matrix (see the Matrix tab) to give A1–A8. A higher Q state reaches a given A class at a lower utilization — a heavily loaded crane fatigues faster than a busy but lightly loaded one.

The example from FEM 9.511: a crane with medium load spectrum, hoisting speed 5 m/min, average hook travel 3 m, 5 cycles per hour, two-shift operation (16 h/day) gives an equivalent daily operating time of 1.6 h — duty class M5 (GB A5, FEM 2m).

Utilization class	Max total work cycles N	Service description
U0	1.6 × 10⁴	Infrequent use
U1	3.2 × 10⁴
U2	6.3 × 10⁴
U3	1.25 × 10⁵	Occasional use
U4	2.5 × 10⁵	Regular light use
U5	5 × 10⁵	Regular intermittent use
U6	1 × 10⁶	Regular busy use
U7	2 × 10⁶	Intensive use
U8	4 × 10⁶
U9	> 4 × 10⁶

Load state	Nominal spectrum factor Kp	Description
Q1 — light	0.125	Rarely lifts rated load; normally light loads
Q2 — medium	0.25	Sometimes lifts rated load; normally moderate loads
Q3 — heavy	0.5	Frequently lifts rated load; normally heavy loads
Q4 — very heavy	1.0	Regularly lifts at or near rated load

Load state ↓ / Utilization →	U0	U1	U2	U3	U4	U5	U6	U7	U8	U9
Q1 (Kp ≤ 0.125)	A1	A1	A1	A2	A3	A4	A5	A6	A7	A8
Q2 (Kp ≤ 0.25)	A1	A1	A2	A3	A4	A5	A6	A7	A8	A8
Q3 (Kp ≤ 0.5)	A1	A2	A3	A4	A5	A6	A7	A8	A8	A8
Q4 (Kp ≤ 1.0)	A2	A3	A4	A5	A6	A7	A8	A8	A8	A8

Cells are clamped to the A1–A8 range per ISO 4301-1:2016 — classes above A8 are collectively rated A8.

Standard	Duty code equivalence
ISO / BS / DIN	M3	M4	M5	M6	M7	M8
GB (China)	A3	A4	A5	A6	A7	A8
FEM	1Bm	1Am	2m	3m	4m	5m
CMAA (US)	A	B	C	D	E	F
HMI	H2	H3	H4	H5	H5	H6
Safe working period SWP (h)	400	800	1,600	3,200	6,300	12,500
Duty cycle %ED	25	30	40	50	60	60
Starts per hour	150	180	240	300	360	360

Based on ISO 4301-1:2016(E), GB/T 3811 and FEM 9.511. This tool gives a design-stage reference; final duty classification should be confirmed by the crane manufacturer against your detailed load spectrum. © Kinocranes.

Crane Duty Classification Calculator

Service life & operating pattern

Load spectrum

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How this calculator works

Step 1 — Total work cycles → utilization class U

Step 2 — Load spectrum → load state Q

Step 3 — Look up working class A

ISO / BS / DIN mechanism class	M6
FEM 9.511 (hoists)	3m
CMAA (US)	D