Does one have to introduce a "speed of spell" to explain the spell blocking? IMHO one has to build up protection before the impact - so how can a wizard react to a spell that is in progress?

4 Answers 4


Spells aren't instant. They take time to move from the end of the wand to the target.

The 6th book explained that an experienced wizard/witch can anticipate and 'know' what the next spell the opponent will use and then cast a deflecting spell accordingly.

  • 4
    Perhaps you might compare it to the duel in The Princess Bride, where Westley and Inigo, as they spar, discuss various fencing moves and their corresponding counter-moves. The idea seems to be that an experienced swordsman can, in a flash, see the beginnings of a particular move and prepare the counter. The same may hold true for spell-casting; we know from the Wingardium Leviosa lesson that some spells involve distinct wand movements.
    – Kyralessa
    Commented Aug 15, 2011 at 4:29
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    And the defensive spells, like the shield, the disarm, etc, tend to be very quick spells to cast: their movements are sharp and quick, their verbal components (if any) are short, and they don't seem to have to be well-aimed.
    – Jeff
    Commented Aug 15, 2011 at 13:29
  • the elaborated defense in Dumbledore/Voldemort duel does not seem to be very simple
    – IljaBek
    Commented Aug 16, 2011 at 21:51
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    @troyaner: Big D and Big V are hardly inexperienced in duels. They are the two most powerful wizards in at least a century. When gods fight, mortals tremble.
    – Jeff
    Commented Oct 20, 2011 at 13:51
  • @Jeff: true, for usual wizards this fight would look not that smooth. though, Dumbledore as well as Voldemort are able actually to defend from each others spells - so there must be some kind of constrain on speed, if both do it at maximum efficiency.... knowing the spell in advance is bit debatable, maybe there are some thought shielding mechanics in place as well
    – IljaBek
    Commented May 17, 2012 at 11:19

The "Protego" spell (the Shield Charm) is given as the foremost personal defense spell; it shields the caster, rebounding minor jinxes back to their caster. It's apparently fast-casting and is the bread and butter counter to a hex, jinx or curse, much like Stupefy (the Stunning Spell) is the bread-and-butter offensive spell (it's unknown which would win; I don't think anyone in the books ever did anything but duck or dodge Stunners). It isn't perfect, though; it must be cast well or a spell can break through it, and the big no-nos, the Unforgivable Curses, are unaffected by a Shield Charm.

There are magical artifacts that have been imbued with shielding spells; the Weasley twins offer several items of clothing in their shop that would shield the wearer like a Shield Charm would, without having to cast it. There are also certain racially-based protections; giants, trolls and dragons are unaffected even by Stunners unless they're strongly cast and well-aimed.


The problem is (as far as we know) a spell has no mass, so it's speed would not depend on the physical strenght of the caster, and we cannot calculate its speed by measuring how long it takes to cross a given distance, for all we know spell volcity can vary according to spell category and indivduals. Speed could even vary according to the distance of the target. If it is pure energy, we could suppose it travels at the speed of light but that is not realistic, wizards would literally need lightning fast reflexes. Plus, the flash of light we see (thought some spell don't produce light, transfiguration and charms especially) may only be a side effect of the spell, or a "tail" only in this case you would see the flash after hearing the thunder.

This is purely speculative but given human reflexes I'd say around 250 kmh as fast as the fastest tennis players can send a ball (world record 263kmh).

It's mostly a matter of anticipating the spell about to be cast at you... and having a good footwork!

  • I just would like to say you don't see a flash AFTER hearing thunder but before.
    – Thomas
    Commented Nov 12, 2015 at 7:05

Protego can be used as the shield charm in all situations except strong magic or the unforgivable curses (avade kedavra, crucio and imperio.) Also, some people say that you turn your wand in a horizontal position when you have to block. It might be true though. I do not get why people in harry potter just do the LCSAB technique to kill people. In other words, levicorpus which dangles the victim in the air, the cast the spell to your victim crucio which they would feel great pain, then use stupefy which will stun them and knock the over. Now you could use the killing curse and bombarda maxima and boom your victim is dead. Sucks how they did not think of that

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