What I do in this instance is to charge higher for the smaller projects and lower for large ones.
For example, for anything 200sqm or less, I’ll charge $10 per sqm.
Between 201 and 500sqm, I’ll charge $8.
From 501 to 1000, I’ll charge $6
Anything above 1000sqm, I’ll charge $5
Something like that. These are just examples of how you can grade your charges for interior design services. You can work out what’s best for your business using this as a guide.