MachineCalcs

Part 103 Ultralight Calculator

Screen an ultralight design against the core 14 CFR Part 103.1 weight, fuel, speed and use thresholds.

Aviation 10 inputs 9 results

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Inputs

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Part 103.1 has separate weight criteria for powered and unpowered ultralight vehicles.
Part 103.1 applies to a vehicle used or intended for manned operation by a single occupant.
Part 103.1 applies to recreation or sport use only.
Part 103.1 requires no U.S. or foreign airworthiness certificate.
Measured empty weight before applying the Part 103 powered-vehicle exclusions entered below.
lb
Powered-vehicle empty weight excludes floats under Part 103.1.
lb
Powered-vehicle empty weight excludes safety devices intended for deployment in a potentially catastrophic situation.
lb
Part 103.1 powered ultralight fuel capacity limit is 5 U.S. gallons.
gal
Use calibrated airspeed at full power in level flight.
kt
Use calibrated airspeed for the power-off stall condition.
kt

Results

Default result
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Failed checks
0
Pass

Also computed

Use checks passed3

3 of 3

Regulated empty weightPass246.0lb

Weight limit254.0lb

Weight marginPass8.0lb

Excluded weight0.0lb

Fuel capacity marginPass0.50gal

Method notes 4 notes
  • Powered screen: regulated empty weight = measured empty weight - excluded floats - excluded emergency safety-device weight.
  • 14 CFR 103.1 powered limits checked here: empty weight less than 254 lb, fuel capacity not over 5 U.S. gal, full-power level speed not over 55 kt CAS, and power-off stall speed not over 24 kt CAS.
  • 14 CFR 103.1 unpowered limit checked here: empty weight less than 155 lb.
  • This is an applicability worksheet only. It is not legal advice, aircraft certification, an airworthiness determination, operating authorization, inspection result or performance approval.

A Part 103 ultralight screen compares entered data with the core 14 CFR 103.1 thresholds. Powered vehicles use regulated empty weight W_reg = W_empty - W_floats - W_safety, then check less than 254 lb, fuel not over 5 U.S. gal, full-power level speed not over 55 kt CAS, and power-off stall not over 24 kt CAS. Unpowered vehicles use the less-than-155-lb empty-weight threshold.

Continue workflow

All Aviation
Next 1 Check aircraft CG Use station weights and arms for a separate CG worksheet after the threshold screen. Next 2 Estimate stall speed Compare entered stall-speed assumptions with lift-equation screening when aerodynamic inputs are known. Next 3 Check density altitude Keep atmosphere context separate from the regulatory threshold arithmetic.

How to use this calculator

  1. Choose powered or unpowered. Select the vehicle type so the correct weight threshold is used.
  2. Answer the use checks. Confirm single-occupant use, recreation or sport use, and no airworthiness certificate.
  3. Enter empty-weight data. Enter measured empty weight and, for powered vehicles, any entered float or emergency safety-device exclusions.
  4. Enter powered limits. For powered vehicles, enter fuel capacity, full-power level speed and power-off stall speed in calibrated airspeed terms.
  5. Read margins. Review failed-check count and each margin before doing any design, documentation or operational review.

How it works

For a powered ultralight, the empty-weight screen is: W_reg = W_empty - W_floats - W_safety The calculator compares that regulated empty weight with the Part 103.1 powered threshold, then reports the remaining margin: margin = limit - entered value

The powered screen also compares entered fuel capacity with 5 U.S. gal, full-power level calibrated airspeed with 55 kt, and power-off stall calibrated airspeed with 24 kt. The unpowered screen uses the 155 lb empty-weight threshold.

Worked example

Verified against the live calculator

A powered design entered at 246 lb measured empty weight, 5.0 U.S. gal fuel, 54 kt full-power level speed and 23 kt power-off stall speed has about 8 lb of weight margin, no fuel margin, about 1 kt of max-speed margin and about 1 kt of stall-speed margin.

Frequently asked questions

What does this Part 103 ultralight calculator check?

It checks the core 14 CFR 103.1 applicability thresholds for powered or unpowered ultralight vehicles: use intent, airworthiness-certificate status, empty weight, and for powered vehicles fuel capacity, full-power level speed and power-off stall speed.

How is powered ultralight empty weight handled?

For the powered screen, the calculator subtracts entered float weight and entered emergency safety-device weight from measured empty weight before comparing the result with the 254 lb threshold.

Does this prove an ultralight is legal to fly?

No. It is only an arithmetic worksheet for the listed Part 103.1 thresholds. Operations, inspection, airspace, lighting, visibility, local interpretation and legal status still require current FAA rules and qualified review.

Should speeds be IAS, TAS or CAS?

Part 103.1 uses calibrated airspeed for the 55 kt full-power level-speed threshold and 24 kt power-off stall-speed threshold, so enter CAS when comparing to the rule language.

Method & assumptions

  • Thresholds are based on 14 CFR 103.1 as checked against the eCFR API snapshot dated 2026-06-02.
  • Speeds are treated as calibrated airspeed because Part 103.1 uses calibrated airspeed language.
  • Float and emergency safety-device exclusions are applied only for the powered vehicle screen.
  • The calculator does not evaluate operations, right-of-way, daylight/visibility/cloud-clearance rules, airspace authorization, inspection, hazardous operation, local interpretation or any non-U.S. rule.
  • This page is not legal advice, airworthiness approval, design approval, inspection signoff or operational authorization.
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