Honestly, you don't need a Speed calculator. Here's a simple way to find out who will attack first:
- Find floor base stat. This is your Base Speed stat plus 5 at Level 100.
- Factor in IVs. IVs add themselves to your stat at Level 100. If you have a 31 IV, that's +31.
- Factor in EVs. EVs add themselves divided by 4 to your stat at Level 100. If you have 252 EVs, that's +63.
- Factor in Nature. Positive natures give x1.1 speed, neutral natures give x1 speed, and hindering/negative natures give x0.9 speed.
- Factor in boosts. Here are how boosts affect your stats:
+1 => x1.5
+2 => x2
+3 => x2.5
+4 => x3
+5 => x3.5
+6 => x4
- Factor in certain moves, abilities, items, and statuses. They are as follows:
Choice Scarf => x1.5
Tailwind => x2
Unburden (When item is consumed) => x2
Swift Swim (In Rainy weather) => x2
Quick Feet (When afflicted by status ailment) => x1.5
Paralysis (On a Pokemon that doesn't have Quick Feet) => x0.5