KSP Delta-v Calculator
Use the Tsiolkovsky rocket equation to estimate your stage performance in Kerbal Space Program.
1) Calculate Δv from Wet and Dry Mass
2) Calculate Fuel Needed for a Target Δv
Tip: Use vacuum Isp for orbital/interplanetary stages and sea-level Isp for atmospheric launch stages.
What is delta-v in KSP?
In Kerbal Space Program, delta-v (Δv) is your spacecraft’s total change in velocity potential. Think of it as your mission budget: launching to orbit, transferring to the Mun, landing, and returning all spend delta-v.
A rocket with high thrust but poor efficiency can still run out of delta-v quickly. A slower, efficient upper stage may carry you much farther. That’s why knowing your stage-by-stage delta-v is crucial for mission planning.
The equation behind this calculator
This calculator uses the classic rocket equation:
Δv = Isp × g₀ × ln(m₀ / m₁)
- Isp = specific impulse in seconds
- g₀ = 9.80665 m/s² (standard gravity constant)
- m₀ = initial (wet) mass
- m₁ = final (dry) mass
This is the same math used by KSP’s in-game engineering display, so it is a reliable way to estimate whether a design can complete a mission profile.
How to use this KSP delta-v calculator
Mode 1: Find Δv from your craft masses
- Enter wet mass (craft plus all fuel at stage start).
- Enter dry mass (craft after fuel is depleted for that stage).
- Enter Isp for the engine setup used in that stage.
- Click Calculate Δv to get total delta-v and mass ratio.
Mode 2: Find fuel needed for a mission segment
- Enter the target delta-v for that segment.
- Enter your final mass (payload, tanks, engine, etc. after burn).
- Enter Isp and calculate.
- The calculator returns required wet mass and fuel mass.
Quick KSP mission planning reference
These are rough planning values (depends on piloting, ascent profile, drag losses, and safety margins):
| Route | Typical Δv (m/s) | Notes |
|---|---|---|
| Kerbin surface → Low Kerbin Orbit | 3400–3800 | Gravity/drag losses vary a lot |
| LKO → Mun intercept | ~860 | Efficient transfer window helps |
| Mun orbit insertion | ~310 | Lower if using aerobraking elsewhere |
| Low Mun Orbit → Mun landing | ~580 | Include landing margin |
| LKO → Minmus intercept + capture | ~930 | Very efficient for science missions |
| LKO → Duna transfer | ~1050 | Window timing matters greatly |
Design tips to get more delta-v
1) Improve mass ratio
Delta-v improves when wet mass is much larger than dry mass. Reducing unnecessary dry mass often helps more than adding fuel.
2) Use better Isp where it counts
High-Isp engines shine in vacuum. Atmospheric engines are usually better during launch because of thrust and sea-level performance.
3) Stage intelligently
Drop dead weight early. Well-designed staging can dramatically increase total mission delta-v.
4) Always add margin
A practical rule: include 10–20% extra delta-v for maneuvers, corrections, and landing safety.
Common mistakes
- Using dry mass that accidentally excludes payload or engine mass
- Using vacuum Isp for a first-stage atmospheric burn
- Planning with zero margin
- Ignoring the cost of inclination changes
Final thoughts
If you can read a delta-v map and run fast stage calculations, KSP gets much easier. Use this calculator as your pre-launch checklist: verify each stage, check transfer costs, and leave margin for the unexpected. Your Kerbals will thank you.