Motor Capacitor Sizing Guide: Complete Charts by Horsepower and Application
Last Updated: February 2026 | Reading Time: 15 minutes
"What size capacitor do I need for a 5 HP motor?" It's one of the most common questions in the capacitor industry — and one of the most dangerous to answer with a single number. Motor capacitor sizing depends on horsepower, voltage, motor type, application, and whether you need a start capacitor, a run capacitor, or both.
This guide provides comprehensive sizing charts for single-phase motors from fractional HP through 15 HP, covering HVAC, industrial, pump, and general-purpose applications. Use these charts as a starting reference, and always verify against the motor nameplate or manufacturer's specification.
Before sizing, make sure you know which type you need:
| Feature | Start Capacitor | Run Capacitor |
|---|
| Purpose | Provides extra starting torque | Improves running efficiency and power factor |
| In circuit | Only during startup (1-3 seconds) | Continuously while motor runs |
| Type | Electrolytic (AC rated) | Oil-filled or dry film (AC rated) |
| Capacitance | High: 70-800+ µF | Low: 1.5-80 µF |
| Voltage | 110V, 125V, 165V, 220V, 250V, 330V AC | 370V AC or 440V AC |
| Failure if oversized | Excessive starting current | Motor overheating, winding damage |
| Failure if undersized | Motor won't start or starts slowly | Reduced efficiency, motor runs hot |
Important: Never use a start capacitor as a run capacitor, and never use a run capacitor as a start capacitor. They are different components designed for different electrical conditions.
The most accurate sizing method is always the motor nameplate or manufacturer's data sheet. Look for:
- Motor nameplate — Usually on a metal plate attached to the motor body
- Existing capacitor label — Read the specifications from the currently installed (possibly failed) capacitor
- Motor data sheet — Available from the motor manufacturer
- Equipment manual — HVAC, compressor, or pump manuals list capacitor specifications
What to look for on the nameplate:
- HP (horsepower) or kW (kilowatts)
- Voltage (115V, 208V, 230V, 460V)
- Full Load Amps (FLA)
- RPM
- Capacitor specification (sometimes listed directly)
- Motor type (PSC, CSIR, CSCR)
- Uses run capacitor only — No start capacitor
- Run capacitor remains in circuit at all times
- Low starting torque
- Common in: fans, blowers, small pumps, light-duty applications
- Uses start capacitor only — No run capacitor
- Start capacitor disconnected after motor reaches ~75% speed
- High starting torque, moderate running efficiency
- Common in: compressors, loaded conveyors, pumps with check valves
- Uses both start and run capacitors
- Start capacitor provides high starting torque
- Run capacitor stays in circuit for efficiency
- Best overall performance
- Common in: HVAC compressors, heavy-duty pumps, industrial motors
These values are typical for general-purpose single-phase induction motors at 230V. Always verify with the motor manufacturer.
| Motor HP | Motor FLA (approx.) | Run Capacitor (µF) | Voltage Rating |
|---|
| 1/8 HP | 1.4A | 2-4 µF | 370V or 440V AC |
| 1/6 HP | 1.8A | 3-5 µF | 370V or 440V AC |
| 1/4 HP | 2.4A | 5-7.5 µF | 370V or 440V AC |
| 1/3 HP | 3.0A | 7.5-10 µF | 370V or 440V AC |
| 1/2 HP | 4.0A | 10-15 µF | 370V or 440V AC |
| 3/4 HP | 5.2A | 15-20 µF | 370V or 440V AC |
| 1 HP | 6.8A | 20-30 µF | 370V or 440V AC |
| 1.5 HP | 9.6A | 25-35 µF | 370V or 440V AC |
| 2 HP | 12A | 30-40 µF | 370V or 440V AC |
| 3 HP | 17A | 35-50 µF | 370V or 440V AC |
| 5 HP | 28A | 45-65 µF | 370V or 440V AC |
| 7.5 HP | 40A | 50-80 µF | 440V AC |
| 10 HP | 50A | 60-80 µF | 440V AC |
Fan motors in HVAC outdoor units are typically PSC type requiring a run capacitor only.
| Motor HP | Fan Motor FLA | Run Capacitor (µF) | Voltage Rating |
|---|
| 1/8 HP | 0.7-1.0A | 2-3 µF | 370V or 440V AC |
| 1/6 HP | 0.9-1.3A | 3-4 µF | 370V or 440V AC |
| 1/4 HP | 1.2-1.8A | 4-5 µF | 370V or 440V AC |
| 1/3 HP | 1.5-2.2A | 5-7.5 µF | 370V or 440V AC |
| 1/2 HP | 2.0-3.0A | 7.5-10 µF | 370V or 440V AC |
| 3/4 HP | 2.8-4.0A | 10-12.5 µF | 370V or 440V AC |
Compressor motors in residential and light commercial HVAC systems typically use CSCR configuration (both start and run capacitors).
| Compressor Size | Run Capacitor (µF) | Voltage Rating |
|---|
| 1.5 ton (18,000 BTU) | 25-30 µF | 370V or 440V AC |
| 2 ton (24,000 BTU) | 30-35 µF | 370V or 440V AC |
| 2.5 ton (30,000 BTU) | 35-40 µF | 370V or 440V AC |
| 3 ton (36,000 BTU) | 40-45 µF | 370V or 440V AC |
| 3.5 ton (42,000 BTU) | 45-50 µF | 370V or 440V AC |
| 4 ton (48,000 BTU) | 45-55 µF | 370V or 440V AC |
| 5 ton (60,000 BTU) | 50-60 µF | 370V or 440V AC |
Dual run capacitors combine the compressor and fan motor capacitors in one can. The most common sizes for residential HVAC:
| Dual Capacitor | Compressor Section | Fan Section | Common Equipment |
|---|
| 25+5 µF | 25 µF | 5 µF | Small 1.5-2 ton systems |
| 30+5 µF | 30 µF | 5 µF | 2-2.5 ton systems |
| 35+5 µF | 35 µF | 5 µF | 2.5-3 ton systems (most common) |
| 40+5 µF | 40 µF | 5 µF | 3-3.5 ton systems |
| 45+5 µF | 45 µF | 5 µF | 3.5-4 ton systems |
| 50+5 µF | 50 µF | 5 µF | 4-5 ton systems |
| 35+7.5 µF | 35 µF | 7.5 µF | Systems with larger fan motor |
| 40+7.5 µF | 40 µF | 7.5 µF | Systems with larger fan motor |
| 45+7.5 µF | 45 µF | 7.5 µF | Larger systems with bigger fan |
| 55+5 µF | 55 µF | 5 µF | Large 5 ton systems |
| 60+5 µF | 60 µF | 5 µF | Commercial light systems |
| Motor HP | Start Capacitor (µF) | Voltage Rating |
|---|
| 1/8 HP | 43-53 µF | 110-125V AC |
| 1/6 HP | 43-53 µF | 110-125V AC |
| 1/4 HP | 75-84 µF | 110-125V AC |
| 1/3 HP | 88-108 µF | 110-125V AC |
| 1/2 HP | 108-130 µF | 110-125V AC |
| 3/4 HP | 130-156 µF | 110-125V AC |
| 1 HP | 161-193 µF | 110-125V AC |
| 1.5 HP | 216-259 µF | 110-125V AC |
| 2 HP | 270-324 µF | 165V AC |
| 3 HP | 324-389 µF | 165V AC |
| 5 HP | 378-454 µF | 220-250V AC |
| Motor HP | Start Capacitor (µF) | Voltage Rating |
|---|
| 1/4 HP | 21-25 µF | 220-250V AC |
| 1/3 HP | 25-30 µF | 220-250V AC |
| 1/2 HP | 30-36 µF | 220-250V AC |
| 3/4 HP | 36-43 µF | 220-250V AC |
| 1 HP | 43-53 µF | 220-250V AC |
| 1.5 HP | 53-64 µF | 220-250V AC |
| 2 HP | 64-77 µF | 220-250V AC |
| 3 HP | 86-103 µF | 220-250V AC |
| 5 HP | 108-130 µF | 330V AC |
| 7.5 HP | 130-156 µF | 330V AC |
| 10 HP | 161-193 µF | 330V AC |
| 15 HP | 216-259 µF | 330V AC |
Hard-start kits for HVAC compressors add a start capacitor and potential relay to give the compressor extra starting torque.
| Compressor Size | Start Capacitor (µF) | Voltage Rating |
|---|
| 1.5-2 ton | 88-108 µF | 220-250V AC |
| 2-3 ton | 108-130 µF | 220-250V AC |
| 3-4 ton | 130-156 µF | 330V AC |
| 4-5 ton | 161-193 µF | 330V AC |
| 5+ ton | 189-227 µF | 330V AC |
Two-wire submersible pumps use a start capacitor (and sometimes a run capacitor) installed in the control box above ground.
| Motor HP | Start Capacitor (µF) | Run Capacitor (µF) | Control Box Voltage |
|---|
| 1/2 HP | — | 15 µF | 230V |
| 3/4 HP | 161-193 µF | 15 µF | 230V |
| 1 HP | 161-193 µF | 20-25 µF | 230V |
| 1.5 HP | 216-259 µF | 25-30 µF | 230V |
| 2 HP | 270-324 µF | 30-35 µF | 230V |
| 3 HP | 324-389 µF | 35-40 µF | 230V |
| 5 HP | 378-454 µF | 45-55 µF | 230V |
Note: Three-wire submersible pumps use a separate control box with integral capacitors. Replace with manufacturer-specified values only.
| Motor HP | Run Capacitor (µF) | Start Capacitor (if equipped) |
|---|
| 3/4 HP | 15-20 µF | 108-130 µF |
| 1 HP | 20-25 µF | 130-156 µF |
| 1.5 HP | 25-30 µF | 161-193 µF |
| 2 HP | 30-35 µF | 216-259 µF |
| 3 HP | 35-45 µF | 270-324 µF |
| Motor HP | Start Capacitor (µF) | Run Capacitor (if PSC) |
|---|
| 1/3 HP | 88-108 µF | 10-15 µF |
| 1/2 HP | 108-130 µF | 15-20 µF |
| 3/4 HP | 130-156 µF | 20-25 µF |
| 1 HP | 161-193 µF | 25-30 µF |
Motor capacitor values should be within ±10% of the specified value. Going outside this range has consequences:
Undersized run capacitor (>10% below spec):
- Reduced motor efficiency
- Higher operating current
- Motor runs hotter
- Shortened motor life
- May not reach full speed under load
Oversized run capacitor (>10% above spec):
- Excessive current in the auxiliary winding
- Motor overheating
- Potential winding insulation damage
- Higher energy consumption
- Can cause the motor to be noisy
Undersized start capacitor:
- Motor may not start under load
- Extended starting time (hard on windings)
- Start relay may not disengage properly
- Humming without rotation
Oversized start capacitor:
- Excessive starting current
- Can damage the centrifugal switch or start relay
- May cause electrical arcing
- Usually less problematic than undersizing (within reason)
You can always use a higher voltage rated capacitor:
| Original Rating | Acceptable Replacements |
|---|
| 370V AC | 370V AC or 440V AC |
| 440V AC | 440V AC only (do not use 370V) |
| 110V AC | 110V, 125V, 165V, or higher |
| 220V AC | 220V, 250V, 330V, or higher |
Higher voltage provides better transient tolerance and often longer life. Never go lower.
| Symptom | Likely Cause |
|---|
| Motor hums but won't start | Start capacitor too small, failed, or missing |
| Motor starts slowly under load | Start capacitor undersized |
| Motor runs hot | Run capacitor wrong size (too large or too small) |
| Motor vibrates excessively | Run capacitor significantly wrong value |
| Capacitor fails repeatedly | Wrong size causing overcurrent, or voltage rating too low |
| High electricity bills | Run capacitor degraded or wrong size (poor power factor) |
| Motor trips overload frequently | Run capacitor value incorrect, motor drawing excess current |
| Compressor short-cycles | Wrong capacitor causing motor protection to trip |
If the original capacitor's label is unreadable:
- Disconnect power to the motor
- Discharge the capacitor safely
- Remove one wire from the capacitor
- Measure with a capacitance meter (most digital multimeters have this function)
- Compare to the charts above based on motor HP and voltage
For run capacitors, a rough estimate can be calculated:
Run Capacitor (µF) ≈ (Motor FLA × 2650) / (Motor Voltage × Motor RPM / 3600)
This is an approximation. Always verify against manufacturer data.
Provide the motor model number and serial number. Most manufacturers can look up the exact capacitor specification.
Within ±10% of the specified value is safe. Going significantly over (20%+) increases current in the auxiliary winding, causing overheating and shortened motor life. The extra "boost" some people expect from a larger capacitor doesn't materialize — it just causes problems.
Yes. The voltage rating is a maximum, not an operating voltage. A 440V capacitor works perfectly in a 370V application and typically lasts longer due to the additional voltage margin. Never go the other direction — never use a 370V capacitor where a 440V is specified.
Yes. Use a 35 µF run capacitor for the compressor and a 5 µF run capacitor for the fan motor. Both should be 370V or 440V AC rated. Wire them separately to the correct motor terminals. This is actually a preferred repair by many HVAC technicians because it allows replacing just the failed section in the future.
Use the HP, voltage, and motor type to reference the charts in this guide. If the motor is a PSC type, you need a run capacitor only. If CSIR, start capacitor only. If CSCR, both. When in doubt, contact the motor manufacturer with the model and serial number.
Check the motor type on the nameplate: PSC = run only, CSIR = start only, CSCR = both. Alternatively, look at the existing wiring: if there's a centrifugal switch or start relay, the motor uses a start capacitor. If there's a capacitor that stays connected at all times, that's a run capacitor.
The first number is the compressor motor section, the second is the fan motor section. A 35+5 has 35 µF for the compressor and 5 µF for the fan. A 40+5 has 40 µF for the compressor and the same 5 µF for the fan. They are not interchangeable — use what the equipment specifies, or within ±10%.
- Always match the motor's specified capacitor value — ±10% tolerance is the safe range
- Higher voltage rating is always acceptable — 440V can replace 370V, but not the reverse
- Start and run capacitors are NOT interchangeable — Different construction, different purpose
- Motor HP alone doesn't determine capacitor size — Voltage, type, and application all matter
- When in doubt, read the nameplate — The motor manufacturer's specification is the final authority
- Dual run capacitors can be replaced with two singles — And vice versa, matching the individual values
- Wrong capacitor size causes motor damage — Undersized won't start, oversized overheats windings
Not sure which capacitor fits your motor? Send us the motor nameplate data — HP, voltage, amps, RPM, and model number — and we'll identify the correct start and/or run capacitor. We stock motor capacitors from fractional HP through 15 HP in all standard voltage ratings, with same-day shipping on in-stock items.
