Speaking at the annual Munich Security Conference just days before the first anniversary of Russia’s invasion, he called on allies to expect a long war.
France’s Emmanuel Macron also said now was not the time for dialogue with Russia over its invasion of Ukraine.
The event is an annual gathering of leaders, officials and diplomats; its focus this year is transatlantic.
US Vice-President Kamala Harris and Secretary of State Antony Blinken are attending with a large congressional delegation, alongside almost 30 European heads of government.
At the conference, Mr Scholz said it was “wise to prepare for a long war” and show Russian President Vladimir Putin that Germany and its allies would not give up on Ukraine.
Ukrainian officials have said they are urgently in need of heavier weapons, and that sufficient battle tanks could help Kyiv’s forces seize back territory from the Russians.
Germany – who in recent months came under growing pressure over its apparent hesitation to send weapons to Ukraine – agreed in January to allow German-made, heavy Leopard tanks to be sent Ukraine.
It also allowed other countries to send their Leopard 2 tanks to Ukraine – which was restricted until now under export regulations.
Mr Macron said the next few weeks would be decisive, adding allies needed to “intensify our support” for Ukraine to be able to launch a counter-offensive, so later the country could enter negotiations in a position of strength.
Earlier, Ukrainian President Volodymyr Zelensky, who spoke to assembled leaders via video link, urged allies to speed up the supply of weapons, warning there was no alternative to victory over Moscow.
No Russian officials have been invited.
The agenda is broad – from China to climate change – but the conference will give Ukraine’s allies a chance to assess Russia’s invasion almost one year on.
There will be warm words of support for Kyiv. But there will also be questions about the extent and duration of Western resolve as economic pressures grow.__BBC.com