How much oil does a gearbox need?

Oil fill depends on gearbox type and size. Empirical: V ≈ k × a² × b, where a = center distance, b = face width. Factor k varies: spur/helical 0.5, bevel 0.6, worm 0.8, planetary 0.35.

What oil level should I maintain?

For splash lube: lowest gear immersed 1-2× tooth height. Worm gears: oil to worm shaft center. Planetary: 1/3 to 1/2 housing height. Always check manufacturer marks.

How does temperature affect oil level?

Oil expands ~0.07% per °C. A 50°C temperature rise on 10 L increases volume by ~350 mL. Fill to cold level mark — hot level will be higher.

What ISO VG grade for gearboxes?

VG 220 for general spur/helical, VG 320-460 for worm or heavy loads, VG 68-150 for high-speed. Follow manufacturer specs.

Should I use synthetic gear oil?

Synthetic (PAO, PAG) recommended for worm gears (higher efficiency), extreme temps, and long intervals. Better VI and oxidation stability. PAG especially good for worm efficiency.

Free Engineering Tool

Gearbox Oil Fill Volume Calculator

Estimate oil quantity for industrial gearboxes. Supports spur, helical, bevel, worm, and planetary types. Oil level at temperature, thermal expansion, drain interval, and oil weight.

5 Gearbox TypesThermal ExpansionDrain IntervalOil Weight

Oil Volume & Specifications

Estimated Oil Fill Volume

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Single Stage Volume

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Oil Weight

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Volume at Operating Temp

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Thermal Expansion

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Type Factor (k)

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Recommended VG Grade

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Oil Level Guidance

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Drain Interval (mineral)

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Drain Interval (synthetic)

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Empirical Oil Volume Formula

Where k is a type-dependent factor, a is center distance (m), b is face width (m). Multi-stage: each additional stage adds ~70% of the first stage volume.

Gearbox Type	Factor k	Fill Ratio	VG Grade
Spur / Helical	0.50	1/3 housing	VG 220
Bevel	0.60	Per marks	VG 220–320
Worm	0.80	To worm center	VG 320–460 (PAG)
Planetary	0.35	1/3–1/2 housing	VG 150–220
Hypoid	0.65	Per marks	VG 220–320 (EP)

Oil Thermal Expansion

Mineral oil expansion coefficient β ≈ 0.0007/°C. Synthetic PAO similar. This means ~7% expansion per 100°C rise.

Practical Example

Example — 2-Stage Helical Gearbox, a=200mm, b=60mm

V₁ = 0.50 × 0.200² × 0.060 × 1000 = 1.20 L

V_total = 1.20 + 1.20 × 0.70 = 2.04 L

Oil weight = 2.04 × 0.87 = 1.77 kg

At 70°C (vs 15°C fill): V_hot = 2.04 × (1 + 0.0007 × 55) = 2.12 L (+79 mL)

Drain Interval Guidelines

Oil Type	Normal (≤70°C)	Warm (70-90°C)	Hot (>90°C)
Mineral (VG 220)	8,000–10,000 h	4,000–6,000 h	2,000–3,000 h
Semi-synthetic	12,000–15,000 h	6,000–10,000 h	3,000–5,000 h
Full synthetic (PAO)	15,000–20,000 h	10,000–15,000 h	5,000–8,000 h
PAG (worm gears)	20,000–30,000 h	12,000–18,000 h	6,000–10,000 h

⚠️ Note: These are approximate empirical values. Always follow the gearbox manufacturer’s specification for actual fill volume and oil grade.

Gear Oil Quantity Calculator | Gearbox Fill Volume | Thermal Expansion | Free Tool

Published by Nikolai Shelkovenko on February 15, 2026 February 15, 2026

Oil Volume & Specifications

Empirical Oil Volume Formula

Oil Thermal Expansion

Practical Example

Drain Interval Guidelines